T-cell-rich B-cell lymphoma in the cat.

The clinical and pathological features of eight cases of feline T-cell-rich B-cell lymphoma are described. The disease occurred in older cats (mean age 11.4 +/- 3.9 years), which on initial examination generally showed enlargement of a single submandibular or cervical lymph node. After excision, there was no recurrence of the lesions at 6 months in three cats. In one further case, however, the lesion had recurred 6 months later; it was again excised but recurred after an additional 6 months. Microscopically, there was effacement of normal lymph node architecture by a nodular (n = 4) or diffuse (n = 4) proliferation of small to blastic lymphocytes, accompanied by a characteristic population of bizarre giant, or multinucleate, cells. The mitotic rate was low and mitoses were restricted to the atypical population. Immunophenotyping revealed the smaller lymphocytes to be a mixture of CD3+ MHC Class II+ T lymphocytes and BLA36+CD79variable MHC Class IIvariable B lymphocytes. The atypical cells were of the B-cell lineage (BLA36+MHC Class IIvariable). Polymerase chain reaction analysis revealed no proviral DNA products of feline leukaemia virus or feline immunodeficiency virus in tissue from any tumour, confirming that these neoplasms were not associated with either virus. The clinical, histological and immunophenotypic findings in these cats were identical with those of "nodular lymphocyte predominance (lymphocytic and histiocytic/L&H) Hodgkin's disease" in man.