The lymphocytic inflammation correlates with metastatic risk in carcinoid tumours

The lymphocytic inflammation inside the neoplastic tissue is widely considered expression of immunological reaction and a prognostic factor. This aspect has been not yet considered in carcinoid tumours and this has been the aim of our study. Our researches have been performed on 20 surgical specimens of carcinoid tumours, including gastrointestinal and bronchopulmonary cases. By immunological techniques, we have studied the presence of B, T and NK lymphocytes inside and around the neoplastic tissue. In carcinoid tumours of our series, the tissue immunological response is independent from their anatomical location. The stromal component, neo-lymphoangiogenesis and macrophage infiltration are always scant or absent. Different subtypes of lymphocytes (CD4+ T-helper, CD8+ T-cytotoxic, CD20+ B) can be present inside the proper neoplastic tissue with the same percentage and not organized in lymphatic centres, or in tertiary lymphatic organs. The lymphocytic inflammation can be quantified into three grades: brisk, not brisk or absent. It has been found independent from the mitotic count and perineural invasion, but it is inversely correlated with the presence of hepatic or lymphatic metastases. The scant presence of immunological reaction represents a tumour immuno-tolerance, likely secondary to an intrinsic histological compatibility, or to the local signaling of suppressor molecular mechanisms. On the contrary, a brisk lymphocytic infiltrate can be interpreted as a host reaction, secondary to a tissue incompatibility or to the release of pro-inflammatory molecules. This immunological aspect of carcinoid tumours deserves to be considered as a significative parameter for the metastatic risk.