Fas, also known as the FAS receptor (FasR), apoptosis antigen 1 (APO-1 or APT), cluster of differentiation 95 (CD95), or tumor necrosis factor receptor superfamily member 6 (TNFRSF6), is a cell surface death receptor that triggers programmed cell death, or apoptosis. In mice, the FasR gene is located on chromosome 19, and orthologous sequences, which are evolutionarily related, are present in most mammals.
Recent research has indicated a dual role for Fas in cancer biology. While it is traditionally associated with the induction of apoptosis, it has also been shown to promote tumor growth. During tumorigenesis, Fas is often downregulated, or tumor cells may develop resistance to apoptosis. Regardless of their sensitivity to Fas-mediated apoptosis, cancer cells generally rely on the constitutive activity of Fas for optimal growth. This activity is often stimulated by the Fas ligand, which is produced by the cancer cells themselves.