Apoptosis and proliferation in subcutaneous panniculitis-like T-cell lymphoma

Subcutaneous panniculitis-like T cell lymphoma (SPTCL), designated recently as a distinct clinicopathologic entity in the World Health Organization Classification, is a neoplasm composed of cytotoxic T-cells that preferentially involves subcutaneous adipose tissue. Histologically, SPTCL is characterized by extensive karyorrhectic debris and tumor necrosis suggesting that apoptotic mechanisms are involved in its pathogenesis. We assessed the apoptotic index (AI) and proliferation rate (PR) of 13 cases of SPTCL by TUNEL test and Ki-67 immunostaining, respectively. We also immunohistochemically assessed for expression of BCL-2 (anti-apoptosis), BAX (pro-apoptosis), and P53 and correlated the results with apoptosis and proliferation. We detected a high AI (median 8.1%) in 11 cases of SPTCL, and 12 cases had low BCL-2 and high BAX expression. BCL-2 expression inversely correlated with AI (P <.001) and BAX (P <.001). We found a low PR (cutoff > or = 25%) in eight (61%) cases. There was an inverse correlation between AI and PR (r = -.58, P =.04). Ten cases were assessed for P53; immunostaining results were heterogeneous but P53 expression correlated with large cell cytologic features. Our findings demonstrate that SPTCLs have a high AI that may be explained by differential expression of BCL-2 and BAX in the neoplastic cells.