[Internal quality control on HER2 status determination in breast cancers: Experience of a cancer center]. / Contrôle de qualité interne de la détermination du statut HER2 dans les cancers du sein : expérience d'un centre de lutte contre le cancer.

INTRODUCTION: The implementation of an internal quality control is mandatory to guarantee the accuracy of HER2 status in invasive breast cancers. OBJECTIVES: To evaluate the impact of our quality control assurance on HER2 status results in invasive breast carcinomas from 2008 to 2014. METHODS: HER2 status was determined by immunohistochemistry as the first-line indication, completed by fluorescence in situ hybridization (FISH) for scores 2+ by immunohistochemistry. Internal quality control of HER2 status relied on the standardization of pre-analytical phases, the use of external controls with a known number of HER2 gene copies determined by FISH and continued monitoring of concordance between immunohistochemistry and FISH. RESULTS: The proportion of HER2-positive cases corresponding to scores 3+ by immunohistochemistry and 2+ amplified by FISH varied from 10.6% to 13.8% (median of 11.3%). The proportion of scores 2+ amplified by FISH varied from 13.3% to 32.7% during period of study. The rate of concordance between FISH and immunohistochemistry for score 0/1+ and 3+ cases were≥97%. Eight among 12 discordant cases were false positive resulting from errors in interpretation of immunohistochemistry (score 2+ instead of 3+). DISCUSSION: Calibration of immunohistochemistry on FISH for HER2 status contributes to limit variability of immunohistochemistry results due to technical issues or interpretation. The implementation of an external control of score 3+ on each slide enables accurate interpretation of score 2+ and 3+ by immunohistochemistry.

Identification of typical medullary breast carcinoma as a genomic sub-group of basal-like carcinomas, a heterogeneous new molecular entity.

INTRODUCTION: Typical medullary breast carcinoma (MBC) has recently been recognized to be part of the basal-like carcinoma spectrum, a feature in agreement with the high rate of TP53 mutations previously reported in MBCs. The present study was therefore designed to identify phenotypic and genetic alterations that distinguish MBCs from basal-like carcinomas (BLC). METHODS: Expression levels of estrogen receptor (ER), progesterone receptor (PR), ERBB2, TP53, cytokeratins (KRTs) 5/6, 14, 8/18, epidermal growth factor receptor and KIT, as well as TP53 gene sequence and high-density array comparative genomic hybridization (CGH) profiles, were assessed and compared in a series of 33 MBCs and 26 BLCs. RESULTS: All tumors were negative for ER, PR and ERBB2. KRTs 5/6 were more frequently expressed in MBCs (94%) than in BLCs (56%) (p = 0.0004). TP53 mutations were disclosed in 20/26 MBCs (77%) and 20/24 BLCs (83%). Array CGH analysis showed that a higher number of gains (95 regions) and losses (34 regions) was observed in MBCs than in BLCs (36 regions of gain; 13 regions of losses). In addition, gains of 1q and 8q, and losses of X were found to be common to the two groups, whereas gains of 10p (53% of the cases), 9p (30.8% of the cases) and 16q (25.8% of the cases), and losses of 4p (34.8% of the cases), and amplicons of 1q, 8p, 10p and 12p were the genetic alterations found to characterize MBC. CONCLUSION: Our study has revealed that MBCs are part of the basal-like group and share common genomic alterations with BLCs, the most frequent being 1q and 8q gains and X losses; however, MBCs are a distinct entity within the basal-like spectrum, characterized by a higher rate of KRT 5/6 expression, a higher rate of gains and losses than BLCs, recurrent 10p, 9p and 16q gains, 4p losses, and 1q, 8p, 10p and 12p amplicons. Our results thus contribute to a better understanding of the heterogeneity in basal-like breast tumors and provide potential diagnostic tools.