Lymphoplasmacytoid lymphoma in a cow.

Lymphoplasmacytoid lymphoma was found in an 8-year-old Holstein cow uninfected with bovine leukemia virus (BLV). The neoplastic tissue was composed of lymphoid and plasmacytoid cells, and intracytoplasmic IgM (lambda) was detected in the latter. The diagnosis was based on the presence of small lymphoid cells and the expression of CD5, which were suggestive of a close relationship with chronic lymphocytic leukemia. Areas of immunoblastoid cells were reminiscent of histologic progression into immunoblastic lymphoma. The neoplastic cells at different stages of differentiation were distinct from those of BLV-associated pleomorphic lymphoma.