Focus on TILs: prognostic significance of tumor infiltrating lymphocytes in human colorectal cancer.

Human colorectal cancer tissues are infiltrated by various immune/inflammatory cells, usually along the invasive margin. These responses tend be regarded as "non-specific". However, it is now clear that these cellular responses, particularly lymphocytic reactions, are independent prognostic factors for a better survival. Immunohistochemical subset analyses have generally disclosed that the number of T-lymphocytes is important. The effects of these T cells tend to be more manifest when the observation periods are longer. These data suggest that some degrees of anti-tumor immunity exist in human colorectal carcinomas. However, human tumors are generally composed of various histologic subtypes, which sometimes complicates these analyses and simple explanations may be misleading. Considered with precaution, these morphologic analyses on immune cell subtypes are important tools to understand the immune responses in human cancers.