Prognostic significance of Ki67 and its correlation with mitotic index in dogs with diffuse large B-cell lymphoma treated with 19-week CHOP-based protocol.

Diffuse large B-cell lymphoma (DLBCL) is the most common type of lymphoma in dogs. We evaluated Ki67 immunoexpression and mitotic index (MI) in dogs diagnosed with DLBCL and treated with a 19-wk CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone) protocol. Twenty-nine lymph node samples from dogs diagnosed with DLBCL were analyzed for Ki67 immunostaining, and positive cells present in 1 cm were counted in a grid reticle for comparison of survival times above and below the means. The Ki67 mean was 107, and the MI mean was 21. There was a significant ( p < 0.05) difference in median survival time between Ki67 immunostaining above and below the mean, with no difference in MI groups. Ki67 values >107 positive cells per 5 HPF counted in a grid reticle were associated with shorter survival times in dogs with DLBCL treated with a 19-wk CHOP-based protocol.