Histologic classification as a prognostic criterion for canine lymphosarcoma.

Neoplastic tissues from 72 dogs with lymphosarcoma were histologically classified according to the Rappaport schema to determine if the histologic features of the disease had any clinical or prognostic importance. Of 72 dogs, lymphosarcomas in 7 were classified as nodular (9.7%) and 65 were classified as diffuse (90.3%). The two principal cytologic types were lymphocytic, poorly differentiated, and histiocytic, which composed 39% and 56% of the lymphosarcomas, respectively; whereas lymphocytic, well differentiated, mixed, and undifferentiated composed 6%. Clinically, all of the dogs were stage III or IV, according to the accepted criteria for canine lymphosarcoma. The overall complete remission rate was 64% and was defined as no clinical evidence of disease after 9 weeks of chemotherapy. Median remission among nodular histiocytic, diffuse lymphocytic, poorly differentiated, and diffuse histiocytic (DH) groups of dogs was 42 days, 29 days, and 42 days (range, 0 to 1,095), respectively. Median survival for the same groups was 235 days, 190 days, and 173 days (range, 1 to 1,261), respectively. A logarithmic analysis of variance revealed no significant differences among nodular histiocytic, diffuse lymphocytic, poorly differentiated, and DH groups relative to days remission, as well as to days survival. It was observed that those dogs with neoplasms classified as DH had longer remission durations. It would appear that for any one animal, histologic classification according to the Rappaport schema cannot be used as a prognostic criterion in predicting therapeutic response, remission, or survival.