What are lymphocytes?
Lymphocytes are a type of white blood cell that play an important role in the immune system by defending the body against disease. Generally, there are two types of lymphocytes: T lymphocytes and B lymphocytes. Each plays their own role in the immune system. Lymphocytes are found all over the body, including the skin. Certain areas of the body (called lymphatic tissues) are rich in lymphocytes. One such area are the lymph nodes.
What is lymphoma of the skin? 
Lymphoma of the skin (or cutaneous lymphoma) is an abnormal replication of lymphocytes that form nodules, plaques, or other lesions within the skin. There are many forms of this condition, including: :
- epitheliotropic lymphoma (sometimes called mycosis fungoides)
- canine cutaneous T-cell lymphoma (CETL)
- non-epitheliotropic lymphoma
What causes this cancer?
The reason why a particular pet may develop this, or any tumor or cancer, is not straightforward. Very few tumors and cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary. In the case of cutaneous lymphoma, no specific risk factors or cause have been identified.
What are the signs of cutaneous lymphoma?
The signs of cutaneous lymphoma vary, depending on the type of lymphoma and where it is located. While single, solitary lesions can occur, cutaneous lymphoma usually appears as multiple, variable-sized irritated, ulcerated, or infected plaques or masses anywhere on the skin. It can especially affect the gums, nose, or lip margins (where the lips meet the skin). These areas may become ulcerated (break open) and bleed or crusted, and secondary infections are possible. This can cause your pet some oral discomfort and/or reluctance to eat.
"The signs of cutaneous lymphoma vary, depending on the type of lymphoma..."
Epitheliotropic lymphoma is the more common form of cutaneous lymphoma. It can look like nodules, plaques, or scabs on the skin. The lesions are usually dry and scaly, with flaking and hair loss (alopecia). Epitheliotropic lymphoma is made of T-cell lymphocytes.
T-cell lymphocytes can produce a protein that causes a higher-than-normal calcium level in the blood (called hypercalcemia). Pets with hypercalcemia may drink and/or urinate more, and kidney damage is possible. They can also feel quite ill and show signs of vomiting or diarrhea when their calcium levels are too high.
Dogs with the non-epitheliotropic form of the disease will have skin nodules or plaques but will often have involvement of the subcutaneous tissues (the tissues found under the skin) as well.
How is this cancer diagnosed?
The easiest way to determine if lymphoma is present is by biopsy of the skin. This is a surgical excision of a piece of the tumor. Pieces of the tumor are then examined by a veterinary pathologist under the microscope. This is called histopathology. Since lymphocytes are naturally present in the skin, and especially present with inflammation and infection, biopsy with histopathology is the most accurate way to make a definitive diagnosis of cutaneous lymphoma.
Other tests may include:
fine needle aspiration of the lesions themselves, or nearby lymph nodes, to examine the cells that are removed. In this case, the pathologist is looking for cancerous lymphocytes that support the diagnosis- baseline blood and urine tests to look for abnormalities in the body’s systems
- chest or abdominal x-rays to look for potential tumour spread
- checking the serum (blood) to look for specific biomarkers that can be elevated in cases of lymphoma (e.g. C-reactive protein)
- PCR testing to help differentiate cancerous lymphocytes from normal but reactive ones.
How does this cancer typically progress?
Regardless of the form of lymphoma, there may be multiple lesions present on your pet's body. These can grow and become increasingly bothersome. They can also spread to other areas of the body, including the lymph nodes (especially those in front of the shoulders, in the armpits, between the legs, and behind the back legs) and the abdominal organs.
What are the treatments for this type of tumor?
By far, the most common treatment for cutaneous lymphoma is chemotherapy. Unfortunately, the response to treatment, although initially encouraging, is typically short-lived, with gradual return of the tumors (usually within 3 months). Although each case is unique, typical survival times for cutaneous lymphoma cases range from 6 months to 2 years.
If your pet no longer responds to therapy, your veterinarian will discuss alternative chemotherapy options or supportive care protocols. These treatments include retinoids (e.g. isotretinoin), linoleic acid, interferon, or prednisone.
In dogs that develop only a single, localized lesion (rare, although reported), surgical removal of the lesion, or radiation therapy, may be helpful.
Is there anything else I should know?
Given that the lesions of cutaneous lymphoma involve the skin, may be readily accessible, and can become bothersome, your pet may be tempted to lick, chew, or scratch. Your pet should not be allowed to lick, chew or scratch any of the affected areas. Prevention of self-trauma is key to managing pets with this disease.
Secondary infection is common with cutaneous lymphoma. This alone can cause significant discomfort for your pet. Your veterinarian may prescribe antibiotics as necessary. If oral lesions are present, they may become dry, cracked and painful, and your pet may be reluctant to eat. Pain medications may be recommended.
