Accelerated Apoptosis and Low Bcl-2 Expression Associated with Neuroendocrine Differentiation Predict Shortened Survival in Operated Large Cell Carcinoma of the Lung

Abstract

In order to test the hypothesis that increased apoptotic activity is connected with neuroendocrine differentiation and low differentiation degree in large cell carcinoma (LCLC) and is regulated by bcl-2 family proteins, we analysed the extent of apoptosis and tumor necrosis and their relation to the expression of bcl-2, bax, bak and mcl-1 in 35 LCLCs, of which 20 were classified as large cell neuroendocrine lung carcinomas (LCNEC) and 15 as large cell non-neuroendocrine lung carcinomas (LCNNEC). The extent of apoptosis was determined by detecting and counting the relative and absolute numbers of apoptotic cells and bodies using in situ 33-end labelling of the apoptotic DNA. The extent and intensity of expression of the bcl-2, bax, bak and mcl-1 proteins were studied by immunohistochemistry. Also the relative volume density of necrosis was evaluated and correlated with the other parameters. Finally, all the parameters were evaluated as prognostic markers and correlated with data on the survival of the patients. Relatively high apoptotic indices were seen in both tumor types (average for both 2.53%, range 0.09—27.01%). Significantly higher bcl-2 and bak indices were detected more often in LCNECs than in LCNNECs. Immunohistochemically detected bax, bcl-2 and bak expression was independent of apoptotic index in both tumor types, while there was a statistically significant positive association between mcl-1 expression and apoptotic index in LCNNEC but not in LCNEC. There was a statistically significant association between high apoptotic index and shortened survival in LCLC. However, no association was found between tumor stage and apoptosis. The patients with LCNEC and low bcl-2 protein expression had a significantly shorter survival time than those with high bcl-2 indices. There was also a clear association between shortened survival and necrotic LCNNEC. LCLCs show relatively high apoptotic activity, which is associated with shortened survival. The expression of bcl-2, bak and mcl- 1 is associated with neuroendocrine differentiation in LCLC. Finally, our results support some previous reports suggesting that bcl-2 expression in combination with some other markers involved in apoptosis and/or proliferation may be of prognostic value in cases of lung carcinoma with neuroendocrine differentiation. Copyright 1999 W.B. Saunders Company Ltd on behalf of the Arányi Lajos Foundation