GCDFP is a prolactin-induced, secretory, actin-binding cytoplasmic protein, also designated glycoprotein (gp) 17. The cells within the body that produce GCDFP-15 appear to be restricted primarily to those with an apocrine function. The protein is found in the acinic cells of the breast, salivary glands and sweat glands as well as vesicula seminalis.
GCDFP can be detected in most breast carcinomas (50-70%) albeit often in a small fraction of tumour cells. Mammary and extramammary Paget’s disease are usually positive. Among sweat gland tumours (particularly apocrine) and salivary gland tumours, GCDFP is frequently expressed. Expression in other adenocarcinomas is very rare, even though a small fraction of cancers of, e.g., the ovary has been reported positive.
In the identification of the unknown primary cancer, GCDFP is a highly specific and fairly sensitive marker for breast carcinoma. The panel should also include Mammaglobin and Estrogen receptor alpha.
Normal skin is an appropriate control: The epithelial cells of the eccrine sweat glands must show the strongest possible cytoplasmic reaction, while all other cells should be negative. A weak background staining can be expected.