Immunohistochemical and ultrastructural localization of T antigen in ovarian tumors

Thomsen-Friedenreich (T) antigen, the immediate precursor antigen of the human blood group MN system, has been found in many carcinomas, but it is suppressed in normal tissues and nonmalignant diseases. Using a monoclonal antibody specific for the T epitope and an indirect immunoperoxidase technique at light and electron microscopic levels, the authors studied the expression of T antigen and its potential diagnostic value in ovarian tumors. Among 30 serous and mucinous ovarian cystadenocarcinomas, 20 (67%) were positive and 10 (33%) were negative for T antigen. In carcinomas, positive rates increased in parallel with the tumor grade and were 37%, 75% and 80% for grade 1, 2, and 3 tumors, respectively. Of the nine patients with metastasis, seven (78%) had positive and two had negative reactions in their primary and metastatic tumors. T antigen staining was observed at the intraluminal cell surfaces and peripheral cell membranes. The ultrastructural localization of T antigen revealed electron-dense reaction products at the cell surface and microvillous surfaces. Of the ten benign ovarian tumors, three (30%) were weakly positive and seven (70%) were negative for T antigen. These findings indicate a positive correlation between the presence of immunoreactive T antigen and conventional unfavorable prognostic indicators in ovarian carcinoma. The surface location of T antigen suggests that it may have a functional role at the cell membrane and the membrane may be involved in secretion (shedding) of T antigen. Detection of T antigen may be a useful marker of prognosis in ovarian carcinoma.