The identification of metastatic
carcinoma of the breast may be difficult in the absence of a previous history of
breast cancer. Various immunophenotypic markers have been introduced to aid in this process. A
monoclonal antibody directed at a 15-kilodalton (kd) gross cystic disease fluid
protein (GCDFP-15) was applied immunohistochemically to
paraffin sections of 105 breast
cancers and 585 nonmammary
malignancies in order to assess its value in this context. In addition, GCDFP-15 was compared with another putative mammary epithelial marker,
alpha-lactalbumin (ALA), with respect to sensitivity and specificity for a diagnosis of
breast carcinoma. Overall, the rates of specificity and sensitivity and the predictive value of a positive result for GCDFP-15 were 95%, 74%, and 74%, respectively. Corresponding statistical parameters for ALA were 50%, 50%, and 23%. A consistent congruency between the reactivity patterns of primary and metastatic breast
cancers was noted for GCDFP-15 but not for ALA. Besides mammary
carcinomas, the major
tumor types that expressed GCDFP-15 were
carcinomas of the salivary glands, sweat glands, and prostate. Since the latter three types of lesions are unlikely to be diagnosed as metastatic
breast cancer, statistical indices were recalculated after exclusion of these three
tumor types. Following this exclusion, the adjusted rate of specificity of GCDFP-15 and the predictive value of a positive result for a diagnosis of metastatic
carcinoma of the breast were each 99%. In contrast, predictive parameters for ALA were not altered. These results show that GCDFP-15 is a specific marker for
breast cancer and is superior to ALA in this respect.