Cutaneous Lymphoma in Dogs and Cats

TL;DR. Cutaneous lymphoma is an uncommon but serious skin cancer in dogs and cats where abnormal white blood cells accumulate in the skin, causing persistent redness, scaling, hair loss, or lumps that can easily be mistaken for chronic allergies.

Cutaneous lymphoma can cause widespread hair loss, redness, and scaling that mimics severe allergies.

What is it?

Cutaneous lymphoma is an uncommon form of cancer that originates in the lymphocytes, which are a specialized type of white blood cell. In a healthy pet, lymphocytes are vital components of the immune system, patrolling the body to identify and destroy infectious invaders. However, when these cells undergo a malignant transformation, they can abnormally accumulate in the skin, leading to a variety of progressive and often painful skin lesions. Because the skin is heavily populated with immune cells, this organ is a primary target for this specific type of lymphoma.

Veterinarians classify cutaneous lymphoma into two primary forms based on how the cancerous cells behave and where they settle within the skin layers:

• Epitheliotropic Lymphoma (Mycosis Fungoides): This is typically of T-cell origin. The term "epitheliotropic" means these malignant cells have a specific attraction to the epidermis, which is the outermost layer of the skin, as well as the epithelial linings of the mouth. This form is characterized by chronic inflammation, scaling, and redness.
• Nonepitheliotropic Lymphoma: This form can arise from either B- or T-lymphocytes. Unlike the epitheliotropic form, these malignant cells do not target the outer layer of the skin. Instead, they accumulate in the deeper layers (the dermis and subcutaneous tissues), typically forming multiple firm, raised nodules or lumps.

Understanding these distinctions is crucial because they influence how the disease presents, how it is diagnosed, and how it progresses over time. A leading veterinary dermatology atlas describes the nonepitheliotropic form as follows:

"Nonepitheliotropic lymphoma is a malignant neoplasm that may arise from B or T lymphocytes. It is uncommon in dogs and cats, with highest incidence in older animals. Usually, nonepitheliotropic lymphoma appears as multiple, firm,"
— Small Animal Dermatology: A Color Atlas and Therapeutic Guide, p. 472

Causes & risk factors

The exact cause of cutaneous lymphoma in dogs and cats remains unknown. Like most cancers, it is believed to result from a complex combination of genetic mutations and environmental factors, though no specific environmental trigger has been definitively linked to the disease. The genetic mutations cause lymphocytes to multiply uncontrollably and migrate to the skin tissues instead of performing their normal immune surveillance.

While any dog or cat can develop cutaneous lymphoma, certain risk factors have been identified:

• Age: This disease is primarily diagnosed in older pets. The risk increases as animals age, with the highest incidence occurring in senior dogs and cats.
• Species: It is considered an uncommon disease in both dogs and cats, though the clinical presentation and progression can vary slightly between the two species.
• Breed Predispositions: In dogs, certain breeds show a higher statistical likelihood of developing this condition, suggesting an underlying genetic susceptibility. These breeds include Boxers, Scottish Terriers, Golden Retrievers, and Rottweilers.

Signs to watch for

The clinical signs of cutaneous lymphoma are highly variable and can mimic many benign skin conditions, such as severe allergies, parasitic infestations, or deep skin infections. This mimicry often leads to delays in diagnosis.

Common Signs

• Pruritus (Itching): Pets often experience moderate to severe itching, leading to scratching, biting, and self-trauma.
• Desquamation and Scaling: The skin may become extremely flaky, dry, and covered in dandruff-like scales.
• Plaques or Nodules: Raised, flat-topped, thickened areas of skin (plaques) or firm, distinct lumps (nodules) can develop. These nodules may be red to purple in color and are often devoid of hair.
• Erythema (Redness): Widespread or localized redness of the skin is a hallmark sign, particularly in the epitheliotropic form.
• Alopecia (Hair Loss): Hair loss can be patchy or widespread, occurring as the cancerous cells disrupt the normal function of hair follicles.

Occasional Signs

• Footpad Hyperkeratosis: The footpads may become abnormally thick, hard, dry, and cracked, which can make walking painful.
• Ulcerative Stomatitis: Painful open sores or ulcers can develop inside the mouth, on the gums, tongue, or inner cheeks.
• Pruritic Exfoliative Erythroderma with Crusting: This is a severe presentation where the skin becomes intensely red, peels constantly, and develops thick crusts.
• Mucocutaneous Depigmentation and Ulceration: The borders where the skin meets mucous membranes—such as the lips, nose, eyelids, and genital regions—can lose their normal dark pigment and develop painful ulcers.
• Doughnut-Shaped Dermoepidermal Mass: Occasional unique, ring-like raised lesions with depressed centers may appear on the skin.
• Peripheral Lymphadenomegaly: The external lymph nodes (such as those under the jaw, in front of the shoulders, or behind the knees) may become enlarged as the disease progresses.

Red-Flag Emergency Signs

While cutaneous lymphoma is primarily a skin disease, it can eventually involve internal organs. You must seek immediate veterinary care if your pet exhibits:

• Severe lethargy or sudden collapse.
• Persistent vomiting or diarrhea.
• Signs of severe abdominal pain (such as a hunched back or guarding of the belly).
• Difficulty breathing.

These signs can indicate systemic spread or severe internal complications, such as an intestinal obstruction or peritonitis caused by the rupture of an internal lymph node or tumor mass.

Mucocutaneous involvement can lead to depigmentation and painful ulcers where the skin meets mucous membranes.

How vets diagnose it

Diagnosing cutaneous lymphoma requires a systematic approach because the symptoms overlap so heavily with common dermatological conditions. Your vet will start with a thorough physical examination, assessing the distribution of the skin lesions and checking for enlarged lymph nodes.

To move toward a definitive diagnosis, your vet will recommend specific diagnostic tests:

Cytology (Fine Needle Aspirate)

Your vet may perform a fine needle aspirate (FNA) of a nodule or plaque. This involves inserting a small needle into the lesion to collect cells, which are then stained and examined under a microscope. While cytology is a valuable, minimally invasive screening tool, it has significant limitations in this disease. A leading veterinary diagnostic manual notes:

"It may only be possible to characterize a tumor as round cell, epithelial, or spindle cell tumor and not as any specific tumor type."
— Diagnostic Cytology and Hematology of the Dog and Cat, p. 104

Because lymphocytes are classified as "round cells," cytology can suggest a round cell tumor but often cannot provide a definitive diagnosis of cutaneous lymphoma, nor can it determine the specific subtype.

Biopsy and Histopathology (The Gold Standard)

A skin biopsy is absolutely essential to confirm a diagnosis of cutaneous lymphoma. Under local anesthesia or general sedation, your vet will remove small, full-thickness circles of skin (punch biopsies) from the affected areas. These samples are sent to a veterinary pathologist for histopathology. The pathologist examines the tissue architecture to see exactly where the abnormal lymphocytes are located. As noted in veterinary literature:

"Distinguishing these requires a biopsy sample to assess the tissue distribution of lymphocytes in relation to the epidermis, and this cannot be done with cytological samples. Nonepitheliotropic lymphoma typically presents with nodules, which may be dermal or subcutaneous, may be alopecic, and may be red to purple in color."
— Diagnostic Cytology and Hematology of the Dog and Cat, p. 104

The biopsy allows the pathologist to confirm whether the cells are infiltrating the outer epidermis (epitheliotropic) or are concentrated in the deeper dermis (nonepitheliotropic), which is critical for determining the prognosis and treatment plan.

Systemic Screening and Staging

Once cutaneous lymphoma is confirmed, your vet will recommend screening for internal organ and lymph node involvement. This staging process helps determine how far the disease has progressed. Staging typically includes:

• Complete Blood Count (CBC) and Biochemistry Profile: To evaluate overall organ function and check for circulating cancerous cells.
• Abdominal Ultrasound: To assess the liver, spleen, and gastrointestinal tract.
• Chest Radiographs (X-rays): To check for enlarged lymph nodes or lung involvement.
• Fine Needle Aspirates of Lymph Nodes: To determine if the cancer has spread to the lymphatic system.

Treatment options

Treatment for cutaneous lymphoma is focused on controlling the disease, reducing discomfort, and extending your pet's quality of life. Because this is a systemic malignant disease, localized treatments are rarely sufficient on their own, though they may be used supportively.

COP Chemotherapy Protocol

The primary treatment for cutaneous lymphoma is systemic chemotherapy. The most common protocol utilized is the COP protocol, which is a combination of three antineoplastic drugs:

• Cyclophosphamide: An alkylating agent that interferes with the DNA of rapidly dividing cancer cells, preventing them from replicating.
• Oncovin (Vincristine): A vinca alkaloid that disrupts cell division (mitosis), causing the cancer cells to die.
• Prednisone (or Prednisolone): A potent corticosteroid that is directly toxic to malignant lymphocytes and helps reduce the severe inflammation and itching associated with the disease.

This combination protocol is designed to attack the cancer cells at different stages of their life cycle while minimizing the side effects associated with high doses of any single drug.

Supportive and Palliative Care

Because the skin barrier is severely compromised by cutaneous lymphoma, secondary bacterial or yeast infections are highly common and cause significant discomfort. Your vet will prescribe:

• Antibiotics or Antifungals: To treat secondary skin infections.
• Medicated Baths: Soothing, antiseptic shampoos to help manage scaling, crusting, and itching.
• Pain Management: Medications to ensure your pet remains comfortable, especially if oral ulcers or deep skin lesions are present.

Prognosis

Cutaneous lymphoma is a slowly progressive but ultimately malignant disease. While temporary remission can often be achieved with chemotherapy, a permanent cure is exceptionally rare. Chronicity and systemic involvement are common features of this disease over time.

The prognosis varies depending on the specific form of lymphoma:

• Epitheliotropic Lymphoma: This form tends to progress slowly, often starting as localized skin scaling and gradually spreading over months to years before involving internal organs. As noted in a prominent veterinary internal medicine textbook:

"Dogs with mycosis fungoides (an epidermotropic T-cell lymphoma) are usually first evaluated because of chronic alopecia, desquamation, pruritus, and erythema, eventually leading to plaque and tumor formation (Fig. 77-2). Mucocutaneous and mucosal lesions are relatively common, but generalized lymph node involvement may not occur initially."
— Veterinary Internal Medicine, p. 1195

• Nonepitheliotropic Lymphoma: This form is often more aggressive. There is usually evidence of systemic involvement early in the course of this form, and the presence of multiple, widespread nodules typically carries a more guarded prognosis.

Your vet will work closely with you to monitor your pet's quality of life, adjusting the treatment protocol as needed to maintain comfort and happiness for as long as possible.

Prevention

Because the exact cause of cutaneous lymphoma is unknown, there are currently no proven prevention strategies, genetic tests, or lifestyle changes that can prevent this disease from developing.

The most effective tool you have is early detection. Regularly inspect your pet's skin during grooming or petting. If you notice persistent redness, scaling, hair loss, or new lumps—especially if they do not respond to standard allergy treatments—schedule an appointment with your vet promptly. Early intervention can significantly improve the success of palliative treatments and extend your pet's comfortable life.

When to call your vet

You should contact your veterinarian if you notice any persistent skin changes in your pet, particularly if they are not improving with standard treatments.

Contact your vet immediately or seek emergency veterinary care if your pet displays any of the following emergency signs:

• Sudden lethargy, weakness, or collapse.
• Severe, persistent vomiting or diarrhea.
• A tense, painful, or distended abdomen.
• Difficulty breathing or rapid, shallow breathing.

These symptoms can indicate that the cancer has spread internally and caused a critical complication, such as an intestinal obstruction or peritonitis. As described in a leading veterinary internal medicine reference:

"Occasionally, signs compatible with an intestinal obstruction or peritonitis (caused by rupture of a lymphomatous mass) occur. Physical examination typically reveals an intraabdominal mass or masses (e. g. , enlarged mesenteric or ileocecocolic lymph nodes or intestinal masses) and thickened bowel loops (in patients with diffuse small intestinal lymphoma)."
— Veterinary Internal Medicine, p. 1195

Prompt medical attention is vital to manage these life-threatening events.

For specific breeds

If you own a Boxer, Scottish Terrier, Golden Retriever, or Rottweiler, you should be extra vigilant regarding skin health. Because these breeds have a higher predisposition to developing cutaneous lymphoma, any chronic skin issues—such as unexplained hair loss, persistent redness, scaling, or the appearance of firm nodules—should be evaluated by a veterinarian without delay. Do not assume that a new skin lump or chronic itch is simply a standard allergy; prompt diagnostic testing, including a skin biopsy, is highly recommended for these at-risk breeds.

Sources

• Veterinary Internal Medicine, 5th Edition, page 1195.
• Small Animal Dermatology: A Color Atlas and Therapeutic Guide, page 472.
• Cowell and Tyler's Diagnostic Cytology and Hematology of the Dog and Cat, 5th Edition, page 104.