Evaluation of morphologic features to identify "basal-like phenotype" on core needle biopsies of breast.

The basal-like phenotype (BLP) subtype of breast carcinoma has been identified as 1 of 5 tumor subtypes first revealed by microarray profiling. This phenotype tends to be more aggressive, is more often associated with BRCA1 mutations, and carries a poor prognosis. Few studies have morphologically characterized BLP on resected breast specimens (RS), and no studies have evaluated these diagnostic parameters in core needle biopsies (CNB) of breast. We identified a group of 35 RS that demonstrated BLP by morphology and/or immunophenotype based on the criteria used in the literature. Retrospectively, we reviewed the CNB of these RS for the following morphologic features: growth pattern, nuclear grade, mitotic rate, presence of ductal carcinoma in situ, necrosis, and lymphocytic response. Of these histologic features, solid growth pattern [88.6% (31/35)] with nuclear grade 3 [100% (35/35)], marked lymphocytic infiltrate [74.3% (26/35)], and absence or <5% of ductal carcinoma in situ [91.4% (32/35)] were seen most consistently in all the CNB. Geographic necrosis was seen in almost half of the cases [48.6% (17/35)]. Lymphovascular invasion and squamoid differentiation were limited to a small number of cases. On the basis of our results, we propose using certain morphologic features (solid growth pattern, high nuclear grade, presence of marked lymphocytic infiltrate, and geographic necrosis) in recognizing BLP on CNB. Triple negativity of estrogen receptor, progesterone receptor, and HER2/neu combined with positive BLP immunohistochemical markers such as the cytokeratins (CK): CK17, CK14, CK5/6, and epidermal growth factor receptor, help to further confirm the diagnosis.