Abstract
Rabbits were immunized with extracts of human ovarian cystadenocarcinomas in an attempt to identify the spectrum of ovarian tumor antigens recognizable by heteroimmune sera. After absorption, the reactivity of the sera with extracts of tumors and normal tissues was examined by double diffusion in agar. Six antigens (OvC‐1, 2, 3, 4, 5 and 6), which could not be detected in normal ovary, were found in a variable proportion of ovarian tumors. Two of these antigens (OvC‐4 and 5) proved to be previously recognized tissue antigens, carcinoembryonic antigen (CEA) and the related normal glycoprotein (NGP). A third antigen (OvC‐3) was shown to be identical to pregnancy‐zone protein (PZP, SP~3~, PAG). It was detected in 20 of 93 epithelial cancers of the ovary and in 20 of 22 sera from ovarian cancer patients. OvC‐6 was an individually specific antigen detectable only in the immunizing tumor. OvC‐1 and OvC‐2 are unrelated to well‐defined tumor antigens. The former was detectable in 48 of 93 epithelial cancers of the ovary, in some cervical, breast, gastric and pancreatic cancers and also in normal kidney and lung. Its presence in cord and pregnancy sera, and in placenta and amniotic fluid, indicates that it may be a new pregnancy‐associated protein. OvC‐2 is confined to ovarian cancers (8/93) and cannot be detected in tumors of other types or in normal adult tissues. Since it is present in placenta, amniotic fluid and fetal intestine it can be considered to be a fetal or differentiation antigen.