Cutaneous lymphoma usually is seen in middle aged to older dogs ranging from 5 and 11 years of age. Unlike other round cell tumors, cutaneous lymphoma usually presents as multiple tumors on the skin as opposed to a solitary mass. Cutaneous lymphoma is divided into epitheliotropic and nonepitheliotropic forms. Epitheliotropic lymphoma is also known as mycosis fungoides (MF), so named because of the mushroom-like morphology of the tumors in humans.
Early stages of epitheliotropic lymphoma can resemble inflammatory skin disease including erythema, scaling, pruritis, depigmentation, alopecia, plaques, ulceration, and crusting. Many dogs are presented with a history of chronic skin disease. The skin lesions may be focal or generalized. Dogs presented with advanced epitheliotropic lymphoma usually have multiple tumors that can occur anywhere, but appear to have a predilection for mucocutaneous junctions and the oral cavity. Metastasis to lymph nodes and other organs occurs, so dogs may present with lymphadenopathy and other signs of systemic disease.
Nonepitheliotropic lymphoma is extremely rare in dogs (but is the more common form of cutaneous lymphoma in cats). It may represent metastatic disease to the skin or a primary skin neoplasm. Multiple, ulcerated, skin nodules are usually observed in this form of the disease. Nonepitheliotropic lymphoma is generally unassociated with erythema, pruritus, and scaling.
Early stages of epitheliotropic lymphoma usually contain a mixture of small- and medium-sized lymphocytes, while the later stages of neoplasia contain mostly large, immature lymphocytes. Individual cell nuclei may be round or have irregular margins that are indented or cleaved. The chromatin pattern is fine and prominent nucleoli are observed. Nonepitheliotropic lymphoma is not as morphologically consistent; neoplastic cells sometimes may be mistaken for poorly differentiated mast cell tumors or histiocytes. Neoplastic lymphocytes are fragile and easily lysed during aspiration and smear preparation. Biopsy often is required for definitive diagnosis.
The prognosis is poor for both forms of cutaneous lymphoma. Recurrence of disease is very common despite various treatment protocols. Generalized epitheliotropic lymphoma is often treated with a five-drug chemotherapy protocol. Palliative therapy, such as glucocorticoid and antibiotic administration as well as antiseborrheic and antibacterial shampoos, can temporarily improve the patient’s quality of life. Retinoids may retard malignant progression, induce remission, and extend life expectancy somewhat.
Focal mycosis fungoides can be treated with surgery or radiation treatment with or without chemotherapy. This form of cutaneous lymphoma has a slightly better prognosis.
Radiation treatment may be helpful, with or without systemic chemotherapy, depending on the stage of disease. In human patients without evidence of systemic disease, total skin electron-beam radiation therapy is very successful in retarding the progression of cutaneous lymphoma.
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