IMMUNOHISTOCHEMICAL STUDY OF C-FOS-POSITIVE LYMPHOCYTES INFILTRATED INTO HUMAN SQUAMOUS-CELL CARCINOMAS OF THE HEAD AND NECK DURING RADIATION-THERAPY AND ITS CLINICAL-SIGNIFICANCE

C-fos has been reported to be one of the immediate early genes in sign al transduction systems after many kinds of stresses, including ionizi ng radiation. Changes in c-fos expression induced by radiation therapy in tumor tissues have not yet been reported. In this study, we have a ttempted to determine whether c-fos expression is induced by radiother apy in human squamous cell carcinomas of the head and neck and to esta blish a possible correlation between c-fos expression and the therapeu tic effects of radiation therapy. Twenty-seven patients with tumors of the oral cavity, oropharynx, and maxillary sinus were examined, all o f which were confirmed as squamous cell carcinomas. After obtaining th e patients' informed consent, biopsies were performed before treatment and at doses of 4, 10, and 20 Gy of radiotherapy, and the specimens w ere preserved in liquid nitrogen for further examination. Serial secti oning of 6 mu m was performed using a cryostat, and samples were immun ohistochemically stained using the streptoavidin-biotin peroxidase met hod and a monoclonal antibody against c-fos. Three of the 27 patients with squamous cell carcinoma showed slight expression of c-fos in thei r tumor cells before and/or at 4 or 10 Gy of radiotherapy. The tumors showed high radiosensitivity. Concerning tumor-infiltrating lymphocyte s, the rate of moderate or remarkable grades of c-fos-positive lymphoc ytes before radiotherapy and at radiation doses of 4, 10, and 20 Gy wa s 8.0, 29.2, 4.8, and 0%, respectively. The relationship between the i mmunohistochemical findings and the antitumor effect at a radiation do se of 20 Gy was examined on the corresponding H&E-stained sections. In patients whose infiltration of c-fos-positive lymphocytes into tumor tissues were moderate or remarkable at 4 Gy of radiotherapy, the tumor s responded significantly well to radiation therapy (P < 0.025, chi(2) test), and the patients took a significantly favorable clinical cours e (P < 0.05, chi(2) test). In a sample from one of the patients, c-fos -positive lymphocytes were identified as CD4 positive and CD8 negative . Therefore, the high radiosensitivity of squamous cell carcinomas in our samples could be explained by an overexpression of c-fos in the tu mor-infiltrating lymphocytes induced by small doses of radiation thera py, and these activated lymphocytes exerted a cytotoxic effect against the cancer cells.