Gross cystic disease fluid protein-15 and mammaglobin A expression determined by immunohistochemistry is of limited utility in triple-negative breast cancer

Aims: In addition to oestrogen and progesterone receptors, gross cystic disease fluid protein-15 (GCDFP-15) and mammaglobin A (MAM) are the most common markers used to identify breast origin by immunohistochemistry. GCDFP-15 expression has been reported in approximately 60% of breast carcinomas and MAM expression in approximately 80%. Data on their expression in triple-negative breast cancer (TNBC) are very limited. The aim of this study was to examine the expression of these markers in TNBC to determine their utility in pathological diagnosis. Methods and results: We studied the immunohistochemical (IHC) expression of GCDFP-15 and MAM in 63 primary and 118 metastatic TNBCs. GCDFP-15 staining was present in 14% of primary and 21% of metastatic TNBCs. MAM staining was present in 25% of primary and 41% of metastatic TNBCs. The frequency of expression of GCDFP-15 and/or MAM was 30% in primary and 43% in metastatic TNBCs, and many positive tumours had only focal staining. Conclusions: Staining for GCDFP-15 and/or MAM in triple-negative carcinomas helps to confirm breast origin, but most tumours in this subgroup of breast carcinomas lack expression of either marker.