Spontaneous Malignant T Cell Lymphoma in a Young Male Common Marmoset (Callithrix jacchus)

We histopathologically and immunohistochemically investigated a case of malignantlymphoma that spontaneously developed in a male common marmoset at two years of age.Beginning at two years four months of age, the animal had an enlargement of thesubmandibular and inguinal lymph nodes, small subcutaneous nodules near the right breastand an approximately fivefold increase in peripheral lymphocyte count compared with theprevious examination value. The postmortem findings at two years eight months of ageshowed lymphadenopathy with enlargement of the thymus and spleen. Small- tointermediate-sized neoplastic lymphocytes had diffusely proliferated in the enlargednodes. The neoplastic cells were pleomorphic and had irregularly shaped nuclei. Thenuclear chromatin staining revealed hyperchromatism in the small-sized cells, and theintermediate-sized cells exhibited vesicular staining. An immunohistochemical examinationindicated that the neoplastic lymphocytes were positive for CD3 and negative for CD20,thus suggesting that they had originated from T cells. In addition, the proliferation ofhigh endothelial venules and reactive epithelioid histiocytes was observed. Scatteredtingible body-laden macrophages were infrequently detected. Neoplastic lymphocytes werealso observed in the thymus, spleen, heart, lungs, liver, kidneys, adrenal glands andfemoral and sternal bone marrow. This malignant lymphoma in a young male common marmosetwas considered to fit the category of “peripheral T-cell lymphoma, not otherwise specified(PTCL-NOS)” according to the new WHO system of classification.