Tumors of the Immune System in Animals

Immune system neoplasia most often involves lymphoid cells but can involve myeloid cells as well. The neoplastic cells may generate a solid tumor or may be circulating in the bloodstream (leukemia).

Lymphomas are common tumors in dogs and cats. The normal adaptive response requires a burst of rapid proliferation of lymphocytes. On occasion, however, this proliferation may be uncontrolled, and lymphoid neoplasms result. Because lymphocytes are present in all organs, lymphoid tumor development can occur in any organ or lymph node. Less commonly, they occur in the eyes, skin, or nose. To determine the stage of the disease, the following tools are useful:

• CBC

• serum chemistry profiles

• abdominal ultrasonography

• abdominal radiography

• bone marrow analyses

Immunofluorescent staining and immunophenotyping can be performed in dogs and cats to characterize lymphomas. They may be either T cell or B cell in origin.

Most cases of canine lymphosarcoma, Marek's disease, calf leukosis, and feline leukemia are of T-cell origin, as are thymomas. Many T-cell lymphomas are associated with a simultaneous immunosuppression manifested by a predisposition to recurrent infections.

Adult bovine and ovine leukosis, alimentary feline leukemia, and avian leukosis are usually of B-cell origin. Under some circumstances, neoplastic B cells may develop into plasma cells.

Plasma-cell tumors are known as myelomas. Because neoplastic plasma cells can secrete immunoglobulins, they give rise to gammopathies.

The treatment and prognosis for neoplasia of the immune system depend on the tumor type, location, and the affected species.