Molecular Classification of Male Breast Cancer Using Immunohistochemistry
G Al-Saati, KC Jensen. King Saud University, Riyadh, Saudi Arabia; Veterans Affairs Palo Alto Health Care System, Palo Alto, CA; Stanford University Hospital, Stanford, CA
Background: Male breast cancer is uncommon, accounting for 0.8% of all breast cancers, but is important given it's association with BRCA1 mutations. A recent gene expression study using RT-PCR showed similar molecular subtypes in male breast cancer as seen in female breast cancer. The purpose of this study is to characterize the molecular subtype of male breast cancer using a panel of immunohistochemical stains.
Design: The records of 25 male breast cancer patients, mean age = 67.7 years (range, 47-84 years) were gathered from two institutions, Palo Alto Veterans Affairs Health Care System and Stanford Hospital. We performed immunohistochemical (IHC) staining for the following antibodies: ER, PR, HER2, EGFR, CK5/6, p63, and calponin. Slides were scored by two observers.
Results: All cases were invasive ductal carcinoma, with two cases also containing an in situ component, as confirmed by intact myoepithelial cell staining by p63 and calponin stains. Staining results and molecular classification are shown in Table 1. Of the 25 cases, 20 (80%) were classified as luminal subtype based on ER reactivity, and lack of HER2, basal cytokeratin, p63 or EGFR staining. Four (16%) were characterized as HER2 subtype based on positive staining results for HER2. One (4%) was classified as basal subtype given a triple negative, basal cytokeratin-positive, p63-positive and EGFR-positive phenotype.