FAS and neoplasm: On the other hand, it is accepted that the main mechanism for which NK-cells act is through inducing apoptosis in the tumor cells [3–6], and we previously obtained in all the tumors of the series (data not shown) variable expression of CD95 (Fas/APO1), a 48-kD transmembrane glycoprotein, at present identified as an important mediator in the apoptotic process mediated by NK-cells.