HAM56 antibody: a tool in the differential diagnosis between colorectal and gynecological malignancy

HAM56, a monoclonal antibody first used to identify macrophages and endothelial cells, also stains many carcinomas (except those arising in the digestive tract). This property is useful in the differentiation between primary ovarian and metastatic colonic carcinomas in the ovary, or between gynecological (ovarian and endometrial) and colonic implants and lymph node metastases. This distinction is important as the prognoses of colorectal and gynecological malignancies differ significantly. Sixteen primary ovarian carcinomas (10 with peritoneal implants and 3 with lymph node metastases), eight cases of primary colonic carcinomas (four metastatic to ovary, four with peritoneal implants, and four with lymph node metastases), and three primary endometrial carcinomas, all with metastases to the ovary, were immunostained with the HAM56 antibody using the ABC immunoperoxidase technique. Linear membranous immunostaining was considered positive, whereas staining of mucin and debris was regarded as negative. Using these parameters, 15/16 ovarian primaries, 9/10 ovarian implants, 3/3 ovarian lymph node metastases, and 3/3 endometrial primaries and their ovarian metastases were positive. Colonic primaries, their ovarian metastases, peritoneal implants, and lymph node metastases were all negative. It is concluded that the HAM56 antibody is a useful tool in the distinction between colorectal and ovarian malignancies in those cases where the routine histological appearance may be ambiguous.