The histologic classification of 602 cases of feline lymphoproliferative disease using the National Cancer Institute working formulation

Case information and histologic slides for 688 admissions of feline tissues from 12 veterinary institutions were assembled and reviewed to determine t issues obtained by biopsy or necropsy, age and sex of cat, tumor topography , feline leukemia viral antigen status, histologic frequency of mitoses, di agnosis, presence of necrosis, and presence and degree of sclerosis. Histol ogic sections were examined to place the lesions in one of the diagnostic c ategories of the National Cancer Institute working formulation (NCI WF) for lymphomas or lymphoid leukemia. Correlations between the various factors d etermined were tested using contingency tables and chi-square analysis to p rovide a statistical comparison between the levels of observations determin ed by case examination with the numbers expected from chance alone. Signifi cant correlations (P less than or equal to 0.05) were found between diagnos is and tumor topography, the frequency of mitoses, necrosis, sclerosis, and age, between mitoses and necrosis, topography, age, and feline leukemia Vi ral infection status, between topography and necrosis and age, and between leukemia Viral status and age. Significant correlations between diagnosis a nd tumor topography included a greater than expected number of cases of acu te and chronic lymphoid leukemia and multicentric distribution of tumor. Sm all cell lymphomas were more frequent than expected in enteric and cutaneou s areas and less frequent than expected in mediastinal, renal, and multicen tric areas. In contrast, the high-grade small noncleaved type of lymphomas was found significantly more frequently than expected in the mediastinum an d less frequently than expected in enteric tissues. In comparing diagnosis and frequency of mitoses, the lymphomas classified as low grade by the NCI WF were significantly more frequent than expected in the lower categories ( 0-2/100X) of mitoses, and those classified as high-grade lymphomas were mor e frequent than expected in the higher categories (4-8/100X) of mitoses. In comparing diagnosis and sclerosis, diffuse sclerosis was more frequent tha n expected for the intermediate grade lymphomas of mixed cell type and for the high-grade lymphomas of the immunoblastic polymorphous type. In compari ng diagnosis and locally extensive necrosis, this feature was more frequent ly observed than expected for cases of intermediate grade lymphoma of the s mall-cleaved cell category and for the high-grade lymphoma of the immunobla stic cell type. In com paring mitoses and necrosis, the lower grade lymphom as were, in general, characterized by a lower frequency of mitoses and a lo wer incidence of necrosis then would be expected from chance alone. In cont rast, the higher grade lymphomas were characterized by more frequent mitose s and a higher incidence of necrosis. In tests comparing mitoses and tumor topography, lymphomas of the alimentary tract were more frequently observed than expected in the category with the lowest level of mitoses (0-1/100X), whereas lymphomas of the mediastinum and kidney were more frequently obser ved than expected in the categories with a higher level (4-20/100X) of mito ses.