Immunoelectronmicroscopic demonstration of surface tumor antigen Ca 125.

Tissue from a serous cystadenocarcinoma of the ovary was incubated with a monoclonal antibody, OC 125, which reacts with a surface tumor antigen in serous, endometrioid, and some clear cell carcinomas of the ovary. Electron microscopic preparation demonstrated the surface nature of the antigen. It is seen as a linear electron-dense deposit that extends onto villous surfaces. It is in some areas focally discontinuous. No other cell structures reacted with the antibody.