An ovarian cancer-associated antigen that crossreacts with a pregnancy-associated protein.

The presence of an ovarian ascitic antigen that crossreacts with a placental antigen was demonstrated in ascitic fluid from patients with advanced ovarian cancer, and the antigen was partially purified. Immunodiffusion and immunoelectrophoresis were employed to confirm the existence of the reactive antigen and to determine the relationships between the antigens from various sources. On double immunodiffusion, the ovarian ascitic antigen was found to be immunologically completely identical with a placental antigen against monospecific antisera raised against an ovarian ascitic and a placental antigen, respectively. On gel filtration on Sephadex G-200, the antigenic activity was eluted in two regions corresponding to different molecular sizes. The two preparations of the larger and smaller forms showed complete identity on double immunodiffusion, but dissimilar mobilities on immunoelectrophoresis. Preliminary characterization of the antigen revealed that it is distinct from several cancer-related antigens so far described.