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 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 theory, but further work would be required to determine if this is a significant factor in the tumour-host interaction.