Evidence for Fas counter attack in vivo from a study of colorectal cancer

Peritumoural cytotoxic lymphocytic infiltrates in colorectal carcinoma may attack tumour cells by expressing Fas ligand and inducing tumour cell apoptosis. However, tumours may mount a 'counter-attack' by down regulating their Fas pathway and expressing Fas ligand themselves to induce apoptosis of lymphocytes. This study used immunohistochemistry to demonstrate the presence of CD8(+) lymphocytes and Fas ligand. The score of CD8(+) peritumoural lymphocytes was negatively correlated with the Fas ligand score of the tumour. The results provide evidence for the Fas 'counter-attack' theory, but further work would be required to determine if this is a significant factor in the tumour-host interaction.