[The role of Fas/FasL system in the regulation of tumor-immune system interactions in papillary thyroid carcinoma in children and adolescents].

Fas(APO-1/CD95) is a transmembrane protein that induces apoptosis in susceptible normal and neoplastic cells upon cross-linking by its ligand (FasL). Changes in the Fas and FasL expression were suggested to be a potential mechanism of tumor immune evasion. Thyroid cancer in children and young adults of the Republic of Belarus is the consequence of the Chernobyl accident. Papillary thyroid cancer (PTC) is the most common variant of thyroid carcinoma. This study was performed on the formalin-fixed and paraffin-embedded tissues obtained after surgery from 43 patients with PTC. The presence of Fas and FasL in thyroid tissue specimens was examined immunohistochemically. Positive staining for FasL was observed on neoplastic thyrocytes, whereas staining of normal thyroid cells was weak or absent. The pattern of staining was membranous and cytoplasmic. Staining of lymphocytes both in tumor tissue and in lymph nodes for FasL was weak or absent. Fas expression was found on normal thyroid cells, cancer cells and lymphocytes both in tumor and in lymph nodes with metastases. In lymph node metastases, in lymphocytes adjacent to FasL cancer cells morphological signs of apoptosis were observed.