Immunohistochemical localization of CA 125 antigen in formalin-fixed paraffin sections of ovarian tumors with the use of Pronase.

The OC 125 monoclonal antibody was used to localize CA 125 antigen in routine paraffin sections of ovarian tumors with the use of a modified avidin-biotin-peroxidase complex (ABC) technic. Pretreatment of the paraffin sections with Pronase allowed subsequent detection of CA 125 antigen. OC 125 stained 4 (80%) of 5 benign and borderline serous ovarian tumors, 12 (86%) of 14 serous adenocarcinomas, and 3 (23%) of 13 benign and malignant mucinous ovarian tumors. The pattern of distribution of CA 125 antigen was mostly at the intraluminal and peripheral cell surfaces, while intracytoplasmic staining also was seen. Overall, CA 125 antigen detectability rate in paraffin sections was found to be compatible with those reported in frozen sections. The method allows retrospective immunohistochemical examination of a large number of cases with ovarian tumors.