Multiple Myeloma in Dogs and Cats: Signs, Diagnosis, Treatment and Prognosis

Multiple Myeloma in Dogs and Cats: Signs, Diagnosis, Treatment and Prognosis

By Dr Duncan Houston

Multiple myeloma can be difficult to recognise because it does not produce one characteristic symptom.

One dog may present with lameness and bone pain. Another may have nosebleeds, sudden blindness or kidney disease. A cat may show little more than weight loss, poor appetite and unusually high globulin levels, despite having substantial plasma cell infiltration within the liver or spleen.

The diagnosis is also more complicated than finding one abnormal protein result. The veterinary team must determine whether the abnormal protein is being produced by cancer, where the malignant plasma cells are located and whether the kidneys, bone marrow, bones, eyes or nervous system are already being affected.

Quick Answer

Multiple myeloma is a systemic cancer of plasma cells, the immune cells responsible for producing antibodies. Cancerous plasma cells may infiltrate the bone marrow, bones and internal organs while producing excessive abnormal immunoglobulins known as paraproteins.

Dogs often develop a classic bone marrow and skeletal form of multiple myeloma. Cats frequently develop broader myeloma-related disorders involving the liver, spleen or other organs, sometimes without marked bone marrow infiltration. Chemotherapy can produce meaningful remission, particularly in dogs, but the outlook varies substantially between species and disease patterns.

What Is Multiple Myeloma?

Plasma cells are specialised B lymphocytes that produce antibodies.

Under normal conditions, many different plasma cell populations produce many different antibodies. This provides broad protection against infectious organisms and other foreign material.

In multiple myeloma, one abnormal plasma cell clone begins multiplying uncontrollably. The malignant cells may:

• Replace normal bone marrow

• Invade bones

• Infiltrate the liver, spleen or other organs

• Produce one abnormal immunoglobulin in very large quantities

• Release immunoglobulin fragments called light chains

• Interfere with normal immunity

• Damage the kidneys

• Increase blood viscosity

• Cause abnormal bleeding

The abnormal immunoglobulin may be called:

• A paraprotein

• Monoclonal protein

• M protein

• M component

• Monoclonal immunoglobulin

Multiple myeloma is systemic disease. It should be distinguished from a solitary plasmacytoma, which is one localised plasma cell tumour arising in the skin, mouth, soft tissue or bone. Localised plasma cell tumours can behave very differently and may respond well to surgery or radiation alone.

Is Multiple Myeloma the Same in Dogs and Cats?

No.

The disease pattern differs enough between dogs and cats that applying the same diagnostic checklist rigidly to both species can miss important cases.

Feature	Dogs	Cats
Typical disease pattern	Bone marrow disease with paraproteinaemia and possible osteolytic lesions	Bone marrow disease, visceral plasma cell infiltration or both
Common internal sites	Bone marrow and skeleton	Spleen, liver, bone marrow and abdominal lymphatic tissues
Bone lesions	Relatively common	Less consistently present
Paraprotein production	Common, but not universal	Common in systemic myeloma-related disorders
Bone marrow involvement	Usually central to diagnosis	May be mild or absent despite substantial systemic disease
Usual first-line chemotherapy	Melphalan with a glucocorticoid	Cyclophosphamide or melphalan with prednisolone, depending on the patient
Broad prognosis	Often months to several years with treatment	More guarded and highly variable

In a modern feline multicentre study, splenic involvement was identified in 86% of assessed cats and hepatic involvement in 71%, while bone marrow plasmacytosis was identified in 63%. This illustrates why a normal or mildly abnormal bone marrow result cannot safely exclude feline myeloma-related disease.

What Other Plasma Cell Disorders Occur?

Multiple myeloma belongs to a larger group called myeloma-related disorders.

These include:

Multiple myeloma

Systemic malignant plasma cell proliferation involving the bone marrow, with paraproteinaemia, light-chain proteinuria, bone lesions or other evidence of organ damage.

Extramedullary plasmacytoma

A plasma cell tumour developing outside the bone marrow.

It may arise in:

• Skin

• Mouth

• Gastrointestinal tract

• Liver

• Spleen

• Lymph nodes

• Other soft tissues

A solitary cutaneous or oral plasmacytoma in a dog may behave relatively benignly after complete removal. Multicentric internal plasmacytoma in a cat may behave more like systemic multiple myeloma.

Solitary osseous plasmacytoma

One plasma cell tumour arising within a bone.

It may cause:

• Local pain

• Lameness

• Spinal cord compression

• Pathological fracture

• A visible osteolytic lesion

Some solitary bone tumours later progress to systemic disease, so long-term monitoring remains necessary.

IgM macroglobulinaemia

A rare disorder in which an immunoglobulin-producing cancer produces large amounts of IgM.

Because IgM is a particularly large molecule, these patients may be highly susceptible to hyperviscosity syndrome.

Immunoglobulin-secreting lymphoma

Some B-cell or lymphoplasmacytic lymphomas produce a monoclonal immunoglobulin and can resemble multiple myeloma.

Plasma cell leukaemia

This is an aggressive form in which large numbers of malignant plasma cells circulate in the peripheral blood.

These conditions overlap biologically, particularly in cats. The exact label matters, but the distribution of disease, organ damage and treatment response often matter even more.

How Common Is Multiple Myeloma?

Multiple myeloma is uncommon in both species.

It accounts for approximately 8% of canine haematopoietic tumours, but only a small proportion of all canine cancers. Most affected dogs are middle-aged or senior, although rare aggressive cases have been reported in young dogs.

Myeloma-related disorders represent less than 1% of feline malignancies and approximately 1.9% of feline haematological cancers. Cats are also usually mature or senior at diagnosis.

The rarity of the disease means that much of the veterinary evidence comes from retrospective studies and small case series rather than large prospective trials.

What Causes Multiple Myeloma?

The cause is usually unknown.

Multiple myeloma probably develops after a plasma cell accumulates several genetic abnormalities that allow it to:

• Divide without normal control

• Avoid natural cell death

• Produce excessive immunoglobulin

• Interact abnormally with bone marrow cells

• Stimulate bone destruction

• Suppress normal immune-cell production

Possible influences include chronic immune stimulation, ageing and individual genetic susceptibility, but no specific food, supplement, vaccine or lifestyle exposure has been proven to cause most cases.

A diagnosis does not mean an owner missed an obvious preventive step.

What Are the Signs of Multiple Myeloma?

The signs depend on where the malignant cells are located and what complications the paraprotein is causing.

Common general signs include:

• Lethargy

• Weakness

• Reduced appetite

• Weight loss

• Muscle loss

• Vomiting

• Diarrhoea

• Increased thirst

• Increased urination

• Dehydration

• Pale gums

• Fever

• Reduced activity

• Reluctance to walk or jump

• Recurrent infections

Signs associated with bone disease include:

• Lameness

• Spinal pain

• Neck pain

• Reluctance to move

• Difficulty climbing stairs

• Difficulty jumping

• Sudden severe limb pain

• Pathological fracture

• Weakness or paralysis caused by spinal cord compression

Signs associated with bleeding include:

• Nosebleeds

• Bleeding gums

• Bruising

• Blood in urine

• Black, tar-like stool

• Vomiting blood

• Bleeding within the eyes

• Prolonged bleeding after blood collection

• Unexplained anaemia

Eye and neurological signs include:

• Sudden blindness

• Dilated pupils

• Retinal haemorrhage

• Retinal detachment

• Disorientation

• Head pressing

• Poor balance

• Seizures

• Collapse

• Reduced consciousness

Dogs with multiple myeloma often present with weakness, lameness, bleeding, ocular abnormalities or increased thirst and urination. Cats more commonly present with lethargy, appetite loss, weight loss, anaemia and abdominal organ involvement.

Can a Pet Have Multiple Myeloma Without Bone Pain?

Yes.

Bone lesions are an important part of canine multiple myeloma, but they are not present in every patient.

Published canine reports have identified bone lesions in approximately 25% to 75% of affected dogs, depending on the population and the imaging method used. CT may detect medullary or skeletal changes that are missed on conventional radiographs.

Bone lesions were identified in fewer than one-third of cats in the recent 50-cat myeloma-related disorder study. Many cats instead had disease affecting the liver, spleen or bone marrow.

The absence of lameness or obvious bone destruction does not rule the disease out.

How Worried Should You Be?

Risk level	What you may notice	What it may mean	What to do
Suspicious but stable	High globulins, mild anaemia, gradual weight loss or one unexplained bone lesion, but still eating and comfortable	Myeloma is one of several possible explanations	Arrange a structured veterinary investigation within the next few days
Moderate concern	Persistent appetite loss, weakness, vomiting, marked hyperglobulinaemia, kidney changes or recurring infections	Systemic plasma cell disease or another serious disorder may be present	Arrange specialist-level investigation promptly
High concern	Significant anaemia, thrombocytopenia, bone pain, nosebleeds, retinal changes or rapidly worsening kidney values	Important organ damage or hyperviscosity may be developing	Seek same-day veterinary assessment
Critical	Sudden blindness, seizures, collapse, inability to stand, breathing difficulty, uncontrolled bleeding or suspected fracture	Life-threatening hyperviscosity, haemorrhage, severe anaemia or spinal involvement	Go to an emergency veterinary hospital immediately

A high globulin concentration alone does not determine the urgency. Vision, neurological function, breathing, bleeding, kidney function and the ability to stand and eat are more important during immediate triage.

Why Does Multiple Myeloma Cause Anaemia?

Anaemia is one of the most common abnormalities in both dogs and cats with systemic myeloma.

Possible causes include:

• Replacement of normal bone marrow by malignant plasma cells

• Chronic inflammation

• Kidney disease and reduced erythropoietin production

• Gastrointestinal or other blood loss

• Abnormal clotting

• Red blood cell destruction

• Reduced nutrition

• Chemotherapy-associated bone marrow suppression

Up to approximately two-thirds of dogs may be anaemic at diagnosis. In the recent feline study, anaemia was reported in 67% of cats and was associated with shorter survival.

A falling red blood cell count should not automatically be attributed to marrow replacement. Bleeding, kidney injury and immune-mediated destruction may require different treatment.

Why Can White Blood Cells and Platelets Become Low?

Heavy bone marrow infiltration can reduce production of:

• Neutrophils

• Other white blood cells

• Platelets

Low white blood cells increase infection risk.

Low platelets can contribute to bruising and bleeding, although the paraprotein itself may also impair platelet function even when the platelet count is not critically low.

Thrombocytopenia was present in 34% of cats in the 2024 study and was associated with a shorter survival time.

A patient with anaemia, thrombocytopenia and abnormal white blood cells has a more concerning pattern than one with an isolated globulin elevation.

What Is Hyperviscosity Syndrome?

Hyperviscosity syndrome occurs when excessive circulating proteins make the blood abnormally thick.

Blood then moves less efficiently through small vessels, reducing oxygen delivery and increasing pressure within delicate vascular beds.

Possible effects include:

• Retinal haemorrhage

• Retinal detachment

• Sudden blindness

• Neurological abnormalities

• Seizures

• Confusion

• Collapse

• Nosebleeds

• Gastrointestinal bleeding

• Kidney dysfunction

• Systemic hypertension

• Cardiac strain

• Congestive heart failure

Hyperviscosity has been reported in approximately one-fifth of dogs with multiple myeloma. It is less well quantified in cats, but severe ocular, cardiovascular and neurological complications have been documented.

Does a very high globulin result always cause hyperviscosity?

No.

Viscosity depends on:

• The concentration of the paraprotein

• The immunoglobulin type

• The shape and tendency of the protein molecules to aggregate

• Hydration

• Red blood cell concentration

• Other circulating proteins

IgM and some polymerised IgA proteins may cause substantial viscosity problems at concentrations that another immunoglobulin might not.

The cat or dog’s clinical signs and retinal findings may therefore be more important than the total protein result alone.

How Does Multiple Myeloma Affect the Kidneys?

Kidney injury may develop through several mechanisms.

Light-chain injury

Some plasma cell tumours produce excessive immunoglobulin light chains.

These small proteins pass through the kidney filtration system and can:

• Injure renal tubules

• Form obstructive casts

• Cause proteinuria

• Contribute to progressive kidney failure

Light chains detected within the urine are commonly called Bence Jones proteins.

Hypercalcaemia

True ionised hypercalcaemia can reduce kidney filtration, increase thirst and urination and promote further kidney injury.

Total calcium can also appear elevated simply because paraproteins bind additional calcium. Measuring ionised calcium helps determine whether biologically active calcium is genuinely increased.

Hyperviscosity and dehydration

Reduced renal blood flow, poor perfusion and dehydration may worsen kidney function.

Concurrent chronic kidney disease

Many affected animals are older and may already have unrelated chronic kidney disease.

Renal disease was a significant negative prognostic factor in a 38-dog melphalan study. Dogs with renal disease had a substantially shorter median survival than dogs without identified renal disease.

Why Does Multiple Myeloma Cause Bone Destruction?

Myeloma cells and the surrounding bone marrow environment release signals that increase osteoclast activity.

Osteoclasts are cells responsible for breaking down bone.

This can create:

• Discrete punched-out lytic lesions

• Diffuse bone loss

• Weakening of vertebrae

• Long-bone lesions

• Pelvic lesions

• Rib lesions

• Pathological fractures

• Spinal cord compression

CT findings in affected dogs have shown that medullary lesions may be bilateral and multifocal, particularly within the humeri, femurs and vertebral column. CT can also identify extradural disease compressing the spinal cord.

Pain can be substantial even when the animal does not cry or react dramatically during examination.

Does Multiple Myeloma Weaken the Immune System?

Yes.

The tumour may produce a huge quantity of one abnormal antibody while suppressing production of the many different normal antibodies needed for effective immune defence.

Bone marrow infiltration and chemotherapy can further reduce immune function.

Affected animals may develop:

• Recurrent bacterial infection

• Urinary infection

• Pneumonia

• Skin infection

• Fever

• Delayed recovery from ordinary illness

A high immunoglobulin concentration does not mean the immune system is working effectively. It may simply mean one useless abnormal immunoglobulin is dominating the blood.

How Is Multiple Myeloma Diagnosed?

There is no single perfect test.

The diagnosis usually requires evidence that a clonal plasma cell population is present and that the disease is affecting the bone marrow, bones, blood proteins, urine or internal organs.

1. Complete Blood Count and Blood Smear

The CBC may identify:

• Nonregenerative anaemia

• Thrombocytopenia

• Neutropenia

• Pancytopenia

• Rouleaux formation

• Circulating abnormal plasma cells

• Evidence of inflammation or infection

Rouleaux describes red blood cells stacked in coin-like chains. Mild rouleaux can occur normally, especially in cats, but marked rouleaux alongside severe hyperglobulinaemia increases concern about abnormal plasma proteins.

The smear also helps determine whether the cells appear mature, atypical, binucleate or highly malignant.

2. Serum Biochemistry

Common abnormalities may include:

• High total protein

• High globulin

• Low albumin-to-globulin ratio

• Azotaemia

• Proteinuria

• Increased total calcium

• Increased ionised calcium

• Liver enzyme abnormalities

• Hypoalbuminaemia

• Electrolyte changes

A normal total protein does not completely exclude multiple myeloma. Light-chain or poorly secretory tumours may produce little visible hyperglobulinaemia, and monoclonal proteins may sometimes be detected despite an apparently normal total protein concentration.

3. Serum Protein Electrophoresis

Serum protein electrophoresis separates the major blood proteins into different fractions.

Monoclonal gammopathy

A narrow, tall peak suggests that one cell clone is producing one dominant protein.

This raises concern for:

• Multiple myeloma

• Plasmacytoma

• Immunoglobulin-secreting lymphoma

• Macroglobulinaemia

• Other clonal B-cell disease

Polyclonal gammopathy

A broad increase involving several immunoglobulins more commonly supports:

• Infection

• Inflammation

• Chronic immune stimulation

• Some liver diseases

Does a monoclonal peak confirm myeloma?

No.

In one feline electrophoresis study, monoclonal gammopathy occurred with splenic plasmacytoma, lymphoma and feline infectious peritonitis. Chronic infection has also occasionally produced monoclonal gammopathy in dogs.

The electrophoresis pattern must be combined with tissue samples and evidence of organ involvement.

4. Immunofixation

Immunofixation can identify the heavy and light chains making up the paraprotein.

This may distinguish:

• IgG

• IgA

• IgM

• Light-chain disease

• Biclonal gammopathy

It can also help reveal a clonal protein that is difficult to appreciate on routine electrophoresis.

Availability varies between veterinary laboratories.

5. Urinalysis and Urine Protein Testing

Urinalysis helps assess:

• Urine concentration

• Protein loss

• Kidney damage

• Urinary infection

• Blood

• Glucose

• Casts

A urine protein-to-creatinine ratio may quantify protein loss.

Urine protein electrophoresis or immunofixation can identify monoclonal light chains.

A negative Bence Jones result does not exclude multiple myeloma. Only a proportion of affected dogs and cats excrete detectable light chains in urine. In the recent feline study, fewer than half of the tested cats had identifiable Bence Jones proteinuria.

6. Bone Marrow Aspiration or Biopsy

Bone marrow sampling evaluates:

• Percentage of plasma cells

• Cell morphology

• Degree of atypia

• Suppression of normal marrow production

• Other possible cancers

• Infection or marrow fibrosis

Plasma cells normally account for only a small proportion of marrow cells.

A large clonal population, marked atypia, binucleation, mitotic activity or replacement of normal marrow strongly supports myeloma.

Can one normal bone marrow sample rule the disease out?

No.

Bone marrow infiltration may be patchy.

This is particularly important in cats, where malignant plasma cells frequently infiltrate the spleen or liver without substantial marrow involvement. A normal marrow aspirate should not end the investigation when paraproteinaemia and organ infiltration remain strongly suspicious.

7. Diagnostic Imaging

Imaging may include:

• Skeletal radiographs

• Whole-body CT

• Targeted CT

• MRI

• Abdominal ultrasound

• Chest imaging

• Echocardiography in selected patients

Skeletal radiographs

Radiographs may show:

• Punched-out bone lesions

• Diffuse osteoporosis

• Vertebral destruction

• Pathological fracture

However, radiographs can miss marrow-centred lesions before enough mineralised bone has been destroyed.

CT

CT is more sensitive for many bone and medullary lesions and may be particularly useful when:

• Bone pain is present

• Neurological signs are present

• Radiographs are normal but suspicion remains high

• A solitary bone lesion must be distinguished from multifocal disease

• Treatment response is being monitored

In one canine series, CT identified intramedullary lesions and extradural disease that would have been difficult to characterise using survey radiographs alone.

MRI

MRI is particularly useful when:

• The brain or spinal cord may be affected

• Vertebral disease is compressing the spinal cord

• A lesion is centred within bone marrow

• Neurological signs cannot be explained by other imaging

Abdominal ultrasound

Ultrasound evaluates the liver, spleen, kidneys, lymph nodes and other abdominal organs.

Normal ultrasound appearance does not completely exclude plasma cell infiltration, particularly in cats. Cytology or biopsy may still be justified when the laboratory pattern strongly supports a myeloma-related disorder.

8. Liver, Spleen or Lymph Node Sampling

Fine-needle aspiration or biopsy may be highly valuable in cats.

In the 2024 feline study, confirmed splenic and hepatic involvement was more common than extensive marrow involvement. Sampling an abnormal liver or spleen may therefore provide the diagnosis when the bone marrow is nondiagnostic.

Cytology may identify:

• Numerous plasma cells

• Marked cellular atypia

• Binucleate cells

• Immature plasmablasts

• Other round-cell tumours

Immunohistochemistry, immunocytochemistry or clonality testing may be required when lymphoma and plasma cell neoplasia are difficult to distinguish.

9. Eye Examination, Blood Pressure and Coagulation Testing

When hyperviscosity or abnormal bleeding is suspected, assessment may include:

• Retinal examination

• Blood pressure

• Coagulation profile

• Platelet count

• Blood smear

• Cardiac assessment

• Serum or plasma viscosity where available

Retinal haemorrhage or unusually tortuous retinal vessels may provide the first visible evidence that the paraprotein is affecting the circulation.

What Diagnostic Criteria Are Used?

Veterinary criteria are not completely standardised, and the correct interpretation differs between species.

Traditional canine criteria

A canine diagnosis is commonly supported when at least two of the following are present:

1. Significant bone marrow plasmacytosis

2. Monoclonal gammopathy

3. Multiple osteolytic lesions

4. Bence Jones proteinuria

Some more recent canine studies have used greater than 20% clonal bone marrow plasma cells, or biopsy-proven osseous or extramedullary plasmacytoma, together with another myeloma-defining feature.

Current feline recommendations

A feline myeloma-related disorder is generally supported by at least two of the following:

1. More than 10% bone marrow plasma cells, or more than 5% markedly atypical plasma cells

2. Paraproteinaemia

3. Osteolytic lesions

4. Light-chain proteinuria

5. Confirmed visceral organ involvement

Including visceral involvement is essential because feline disease frequently affects the liver or spleen without extensive bone marrow disease.

What Else Can Look Like Multiple Myeloma?

Several diseases can produce high globulins, cytopenias, bone lesions or abnormal plasma cells.

Chronic Infection or Inflammation

Possible causes include:

• Tick-borne disease

• Leishmaniasis in endemic areas

• Chronic bacterial infection

• Fungal disease

• Severe dental infection

• Chronic inflammatory disease

• Feline infectious peritonitis

These disorders more commonly produce a polyclonal gammopathy, but occasional monoclonal patterns occur.

Lymphoma

B-cell or lymphoplasmacytic lymphoma may:

• Produce a monoclonal immunoglobulin

• Infiltrate the marrow

• Affect liver and spleen

• Cause cytopenias

• Resemble a plasma cell neoplasm cytologically

Immunophenotyping and tissue architecture may be needed to distinguish them.

Reactive Plasmacytosis

Plasma cells increase normally during chronic immune stimulation.

A modest number of mature-looking plasma cells within the marrow, lymph node, liver or spleen does not automatically indicate cancer.

The degree of atypia, percentage of cells, protein pattern and clinical distribution all matter.

Monoclonal Gammopathy Without Identified Cancer

Rare animals may have a monoclonal protein without immediate evidence of organ damage or a demonstrable plasma cell tumour.

These patients require monitoring rather than automatic chemotherapy.

Other Bone Tumours

Osteolytic lesions may also be caused by:

• Osteosarcoma

• Lymphoma

• Metastatic carcinoma

• Bone infection

• Fungal disease

• Other marrow tumours

Kidney Disease

Kidney disease can cause:

• Anaemia

• Proteinuria

• Increased thirst

• Weakness

• Weight loss

The presence of kidney disease does not prove that myeloma is responsible, and the presence of myeloma does not mean every renal abnormality is paraprotein-related.

How Is Multiple Myeloma Treated?

Treatment is designed to:

• Reduce the malignant plasma cell population

• Lower the paraprotein concentration

• Restore normal bone marrow production

• Relieve bone pain

• Protect kidney function

• Control hyperviscosity

• Treat bleeding or infection

• Preserve quality of life

Systemic multiple myeloma requires systemic chemotherapy.

Treatment in Dogs

Melphalan combined with a glucocorticoid remains the established first-line treatment for most dogs.

Melphalan may be given using:

• A continuous lower-dose schedule

• A pulse-dose schedule

• A cyclical schedule selected by the oncologist

Published canine studies have shown that most dogs achieve at least a partial response. Median survival has ranged from approximately 540 days in an older cohort to 930 days in a more recent 38-dog study. Daily and pulse-dose melphalan produced similar outcomes in the 2018 study.

What are the risks of melphalan?

Potential adverse effects include:

• Neutropenia

• Thrombocytopenia

• Anaemia

• Reduced appetite

• Vomiting

• Diarrhoea

• Cumulative bone marrow suppression

• Increased infection risk

Regular CBC monitoring is essential because delayed myelosuppression may develop after the dog has been taking the medication for some time.

What if melphalan stops working?

Rescue options may include:

• Cyclophosphamide

• Chlorambucil

• Lomustine

• Doxorubicin

• Other specialist-selected chemotherapy

• Radiation for focal painful disease

• Clinical trials or investigational treatment

The choice depends on previous treatment, kidney function, blood counts and the pattern of relapse.

Treatment in Cats

There is no universally established feline protocol.

Options include:

• Cyclophosphamide with prednisolone

• Melphalan with prednisolone

• Chlorambucil with prednisolone

• Other systemic chemotherapy selected by an oncologist

A 2024 multicentre study reported response rates of 87% with melphalan and 90% with cyclophosphamide when each was combined with prednisolone. However, adverse effects were reported more frequently with melphalan than cyclophosphamide, and the overall feline prognosis remained guarded.

Cyclophosphamide with prednisolone may therefore be considered a useful first-line feline option, particularly when avoiding cumulative melphalan-associated marrow toxicity is a priority. Individual cats may still benefit from melphalan or chlorambucil.

Why are feline outcomes different?

Possible reasons include:

• More frequent visceral disease

• Advanced disease at diagnosis

• Greater biological diversity

• Anaemia and thrombocytopenia

• Kidney dysfunction

• Treatment toxicity

• Small and heterogeneous study populations

Cats should not be given a canine prognosis simply because the tumour cells have the same name.

Can Radiation Therapy Help?

Yes.

Radiation therapy may be used for:

• One painful osteolytic lesion

• Vertebral disease

• Spinal cord compression

• A solitary osseous plasmacytoma

• A local tumour that cannot be removed surgically

• Residual local disease

• Palliative pain control

In a study of 30 dogs with macroscopic plasma cell tumours, 95% of evaluable dogs achieved a complete or partial response to radiation. Dogs receiving radiation for multiple myeloma-associated bone lesions experienced meaningful pain relief.

Radiation treats the targeted area. It does not replace systemic chemotherapy when multiple myeloma is affecting the rest of the body.

When Is Surgery Used?

Surgery is not a primary treatment for systemic multiple myeloma.

It may be useful for:

• A solitary cutaneous plasmacytoma

• A solitary oral plasmacytoma

• A local gastrointestinal plasmacytoma

• A solitary bone lesion that can be removed

• A pathological fracture

• Spinal instability

• Obtaining diagnostic tissue

A dog with a genuinely solitary osseous plasmacytoma may have a substantially better prognosis than a dog with systemic multiple myeloma. One 13-dog study reported a median survival of 912 days, increasing to 1,166 days among dogs completing radiation therapy.

Complete staging is needed before describing a lesion as solitary.

How Is Hyperviscosity Treated?

A patient with severe hyperviscosity may require emergency hospitalisation.

Treatment may include:

• Carefully planned intravenous fluids

• Oxygen

• Blood pressure management

• Seizure treatment

• Treatment of heart failure

• Rapid initiation of chemotherapy

• Therapeutic plasma exchange or plasmapheresis

Plasma exchange removes paraprotein-containing plasma from circulation and replaces it with appropriate fluid or plasma products.

This can improve viscosity-related signs more quickly than chemotherapy, but the benefit is temporary because the malignant cells continue producing abnormal protein. A canine case report documented temporary resolution of hyperviscosity signs following double-filtration plasmapheresis.

Plasmapheresis is generally used as a bridge while chemotherapy begins controlling the tumour.

When Is a Blood Transfusion Needed?

A red blood cell transfusion may be required when myeloma causes:

• Severe symptomatic anaemia

• Active haemorrhage

• Collapse

• Marked weakness

• Cardiovascular instability

• Breathing changes caused by poor oxygen delivery

Platelet-containing products may be considered during life-threatening thrombocytopenic bleeding, although availability is limited.

A transfusion treats the immediate consequences of blood-cell loss. It does not treat the plasma cell cancer itself.

How Is Kidney Disease Managed?

Kidney support may include:

• Correcting dehydration

• Avoiding nephrotoxic medication

• Managing hypertension

• Monitoring urine protein

• Treating hypercalcaemia

• Treating urinary infection

• Renal nutrition when appropriate

• Adjusting chemotherapy

• Managing nausea and appetite loss

Fluid treatment must be individualised. A dehydrated patient may benefit, while a hyperviscous patient with cardiac compromise can deteriorate if fluids are administered without appropriate monitoring.

How Is Bone Pain Managed?

Pain management may include:

• Opioid medication

• Gabapentin or another neuropathic pain medication

• Radiation therapy

• Stabilisation of a fracture

• Surgery in selected cases

• Restricted activity

• Supportive bedding and mobility assistance

Non-steroidal anti-inflammatory drugs require particular caution because myeloma patients may have kidney disease, thrombocytopenia, platelet dysfunction or gastrointestinal bleeding.

Never give ibuprofen, naproxen, diclofenac or another human pain medication to a dog or cat without specific veterinary instructions.

Are There New or Experimental Treatments?

Treatment options used routinely in human myeloma are being investigated in veterinary patients, but evidence remains limited.

A 2026 multicentre study examined thalidomide as rescue treatment in seven dogs that had become resistant to or intolerant of standard treatment. Five dogs achieved or maintained a complete response, and median progression-free survival during thalidomide treatment was 490 days.

This is encouraging, but seven dogs are not enough to establish thalidomide as a routine first-line treatment. Larger prospective studies are still needed.

Other investigational or rescue treatments may include proteasome inhibitors, immunomodulatory drugs and additional chemotherapy combinations. These should be managed through a veterinary oncologist.

How Is Treatment Response Monitored?

Monitoring should assess the tumour and the patient.

Laboratory monitoring may include:

• Complete blood count

• Total protein

• Globulin

• Albumin

• Serum protein electrophoresis

• M-protein measurement

• Kidney values

• Calcium

• Liver values

• Urinalysis

• Urine protein-to-creatinine ratio

• Urine protein electrophoresis

Clinical monitoring includes:

• Appetite

• Body weight

• Energy

• Pain

• Lameness

• Thirst

• Urination

• Bleeding

• Vision

• Neurological function

• Infection

• Medication tolerance

Imaging may include:

• Repeat CT

• Targeted radiographs

• MRI

• Ultrasound

• Chest imaging

When possible, the individual M protein should be followed rather than relying only on total globulin.

Globulin can change because of hydration, inflammation or other disease. The abnormal monoclonal component is a more specific marker of tumour response.

What Does Remission Mean?

A complete response may include:

• Resolution of clinical signs

• Normalisation or disappearance of the M protein

• Recovery of blood-cell counts

• Improvement in organ function

• No measurable progression on imaging

A partial response means that the tumour burden or paraprotein concentration has decreased substantially but disease remains detectable.

Stable disease means that the condition has not meaningfully improved or progressed.

Progressive disease means:

• The M protein rises

• New lesions appear

• Existing lesions enlarge

• Blood-cell counts worsen because of disease

• Clinical signs return

Multiple myeloma is generally considered manageable rather than permanently curable. Even a patient in complete clinical remission requires continued monitoring.

What Is the Prognosis for Dogs?

Dogs often respond well to treatment.

A 2018 study of 38 melphalan-treated dogs reported:

• Median overall survival of 930 days

• Similar outcomes with daily and pulse-dose melphalan

• Shorter survival in dogs with renal disease

• Shorter survival in dogs with a higher neutrophil-to-lymphocyte ratio

An older cohort reported a median survival of 540 days with melphalan-based treatment.

These results indicate that many dogs can enjoy one to several years of useful quality of life after diagnosis.

The outlook is more guarded when there is:

• Renal disease

• Severe hyperviscosity

• Major bleeding

• Extensive marrow failure

• Aggressive or refractory disease

• Inability to tolerate chemotherapy

• Significant neurological impairment

• Poor initial treatment response

Bone lesions and hypercalcaemia were not negative prognostic factors in the 2018 study, although they still require treatment and can significantly affect comfort.

What Is the Prognosis for Cats?

The feline prognosis is generally more guarded and less predictable.

In the 2024 multicentre study of 50 cats:

• Overall median survival was 122 days

• Median survival among cats initially treated with melphalan or cyclophosphamide plus corticosteroids was 315 days

• Individual survival ranged from no survival after diagnosis to more than 1,400 days

• Anaemia and thrombocytopenia were associated with shorter survival

Cats without anaemia or thrombocytopenia had substantially better outcomes than cats already experiencing these complications.

These findings are more guarded than older claims that feline multiple myeloma routinely carries a median survival of approximately 12 months.

Some cats still achieve meaningful long-term control. Others deteriorate rapidly because of extensive visceral disease, marrow failure, hyperviscosity or kidney injury.

Comparing Prognosis in Dogs and Cats

Disease pattern	Broad published outcome	Important limitation
Canine multiple myeloma treated with melphalan	Median survival approximately 540 to 930 days	Outcomes vary with renal disease, treatment response and study population
Feline systemic myeloma-related disorder	Overall median survival 122 days in a recent study	Cats had varied disease patterns and some were untreated or severely ill
Feline cases receiving melphalan or cyclophosphamide with corticosteroids	Median survival 315 days	Retrospective data with small treatment groups
Canine solitary osseous plasmacytoma	Median survival approximately 912 days	Not the same disease as systemic multiple myeloma
Localised cutaneous or oral plasmacytoma	May be controlled for years after appropriate local treatment	Complete staging is needed to confirm that disease is truly localised

Published medians describe groups. They are not individual expiry dates.

When Is Multiple Myeloma an Emergency?

Go to an emergency veterinary hospital immediately if your dog or cat develops:

• Sudden blindness

• Very large or unequal pupils

• Seizures

• Severe disorientation

• Collapse

• Inability to stand

• Open-mouth breathing

• Marked breathing effort

• Blue or grey gums

• Extremely pale gums

• Uncontrolled bleeding

• Vomiting blood

• Black, tar-like stool with weakness

• Sudden severe lameness

• Suspected fracture

• Severe spinal pain

• Sudden paralysis

• Profound weakness

• Reduced consciousness

• Rapid deterioration over several hours

These signs may indicate:

• Hyperviscosity syndrome

• Retinal haemorrhage

• Central nervous system bleeding

• Severe anaemia

• Pathological fracture

• Spinal cord compression

• Kidney failure

• Cardiac failure

• Major infection

• Treatment toxicity

Do not wait for the next scheduled oncology appointment when vision, breathing, bleeding or neurological function is unstable.

What Should You Do Next?

1. Obtain the complete laboratory results

Ask for copies of:

• CBC

• Blood-smear interpretation

• Biochemistry

• Total protein

• Albumin

• Globulin

• Calcium

• Kidney values

• Urinalysis

• Urine protein-to-creatinine ratio

Look at the trend rather than one result in isolation.

2. Ask whether serum protein electrophoresis has been performed

A high globulin result is only the beginning of the investigation.

Ask whether the pattern is:

• Monoclonal

• Biclonal

• Polyclonal

• Equivocal

Ask whether immunofixation is available.

3. Determine where the malignant cells are located

Discuss whether the patient needs:

• Bone marrow aspiration

• Bone marrow biopsy

• Liver sampling

• Spleen sampling

• Lymph node sampling

• Biopsy of a mass

• Full-body CT

• MRI

• Targeted skeletal imaging

Cats in particular may require liver or spleen sampling despite a nondiagnostic marrow result.

4. Assess for hyperviscosity

Ask whether the patient needs:

• Retinal examination

• Blood pressure

• Coagulation testing

• Cardiac evaluation

• Blood-viscosity testing

• Emergency plasmapheresis referral

5. Assess kidney and bone complications

Check:

• Creatinine and SDMA

• Urine concentration

• Proteinuria

• Ionised calcium

• Bone pain

• Neurological function

• Risk of fracture

6. Request oncology or internal medicine referral

Referral is especially valuable when:

• The diagnosis remains uncertain

• A monoclonal gammopathy is present

• Bone marrow or organ samples contain atypical plasma cells

• Hyperviscosity is suspected

• Chemotherapy is being considered

• Radiation may relieve bone pain

• A solitary lesion may be surgically removable

• The disease has relapsed

Referral provides clearer options. It does not commit the family to aggressive treatment.

7. Decide on the treatment goal

The treatment may aim to:

• Achieve remission

• Lower the paraprotein

• Relieve bone pain

• Restore blood-cell production

• Protect kidney function

• Stabilise hyperviscosity

• Maintain appetite and activity

• Provide comfort-focused care

8. Create an emergency plan

Know:

• Which signs require an immediate visit

• Where the nearest emergency hospital is

• Whether transfusion is available

• Whether plasmapheresis is available

• What to do if the patient stops eating

• What to do after vomiting chemotherapy

• Who to contact after hours

Common Mistakes Owners and Veterinary Teams Should Avoid

Assuming every high globulin result means multiple myeloma

Infection, inflammation, lymphoma and several other disorders are more common.

Assuming one monoclonal peak confirms the diagnosis

Monoclonal gammopathy supports clonal immunoglobulin production but does not identify the exact cancer by itself.

Assuming a normal total protein rules myeloma out

Light-chain, poorly secretory or nonsecretory disease can occur.

Assuming negative Bence Jones proteinuria rules the disease out

Many affected dogs and cats do not have detectable urinary light chains.

Stopping after a normal skeletal radiograph

CT may identify marrow and bone lesions that conventional radiographs miss.

Stopping after one normal bone marrow sample in a cat

Feline disease frequently involves the liver or spleen without substantial marrow infiltration.

Starting corticosteroids before obtaining useful samples

Steroids can temporarily alter tumour-cell appearance and interfere with later diagnosis.

Treating a solitary plasmacytoma as though it must be systemic myeloma

Localised plasma cell tumours may have a much better prognosis and may respond to surgery or radiation.

Treating systemic myeloma with surgery alone

Removing one visible lesion does not control malignant plasma cells throughout the body.

Monitoring total protein without measuring the M protein

Total globulin may be influenced by inflammation, hydration and unrelated disease.

Comparing a cat’s prognosis directly with a dog’s

Current feline evidence is considerably more guarded.

Ignoring eye or neurological changes

Sudden blindness, seizures or confusion may indicate life-threatening hyperviscosity.

Can Multiple Myeloma Be Prevented?

There is no proven method of preventing multiple myeloma in dogs or cats.

Practical measures that may support earlier detection include:

• Regular senior health examinations

• Periodic CBC and biochemistry testing

• Investigating persistent hyperglobulinaemia

• Investigating unexplained anaemia or thrombocytopenia

• Assessing recurring infections

• Investigating persistent bone or spinal pain

• Checking sudden vision changes immediately

• Monitoring unexplained proteinuria

• Biopsying unusual plasma cell tumours

• Following up monoclonal gammopathy rather than ignoring it

Earlier diagnosis may allow treatment before severe kidney failure, marrow suppression, fracture or hyperviscosity develops.

Frequently Asked Questions

Can multiple myeloma in dogs or cats be cured?

Systemic multiple myeloma is rarely considered permanently curable. Chemotherapy can produce remission and a good quality of life, particularly in dogs, but relapse commonly occurs. Some solitary plasma cell tumours may be cured with complete local treatment.

Does every patient with multiple myeloma have bone lesions?

No. Bone lesions are common in dogs but are not universal. Cats frequently have liver or spleen involvement without obvious skeletal disease.

Does a monoclonal gammopathy always mean cancer?

No. It strongly raises concern for a plasma cell or B-cell cancer, but occasional infections, inflammatory diseases and apparently benign gammopathies can produce a monoclonal pattern.

Is multiple myeloma painful?

It can be very painful when bone destruction, fracture, spinal compression or organ enlargement is present. Other patients show little obvious pain despite substantial systemic disease.

How long can a dog or cat live with multiple myeloma?

Treated dogs commonly have median survival measured between approximately 18 months and 2.5 years in published studies. A recent feline study reported an overall median of 122 days and approximately 315 days among cats receiving common first-line chemotherapy combinations. Individual outcomes vary from days to several years.

Final Takeaway

Multiple myeloma is a systemic plasma cell cancer that can affect the bone marrow, bones, kidneys, liver, spleen, eyes, nervous system and clotting system.

Dogs often develop the classic combination of bone marrow plasmacytosis, monoclonal gammopathy and osteolytic bone disease. Cats are different. Significant liver or spleen infiltration may occur even when bone marrow involvement is mild or absent.

The safest diagnostic approach is systematic:

• Determine whether the abnormal protein is monoclonal

• Identify where the malignant plasma cells are located

• Assess the bone marrow and blood-cell counts

• Evaluate the kidneys

• Look for bone lesions

• Check for hyperviscosity and bleeding

• Distinguish systemic myeloma from a solitary plasmacytoma

Dogs often respond well to melphalan-based chemotherapy and may remain comfortable for several years. Cats can also respond, but current feline evidence supports a more guarded prognosis and greater attention to anaemia, thrombocytopenia and visceral disease.

Most importantly, sudden blindness, seizures, collapse, breathing difficulty, major bleeding, severe bone pain or suspected fracture should be treated as emergencies.

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If you are unsure what your pet’s globulin result, protein electrophoresis, bone marrow findings or plasma cell diagnosis means, ASK A VET™ can help you organise the results and prepare the right questions for your veterinarian.