Histological grade concordance between diagnostic core biopsy and corresponding surgical specimen in HR-positive/HER2-negative breast carcinoma

BACKGROUND: The identification and validation of suitable predictive and prognostic factors are a challenge to improve the treatment scheme selection. Discordances in histological grade can be established between core biopsy and surgical specimens. This is important in HR-positive/HER2-negative subgroup where histological grade identifies patients at high risk and is a strong determinant for treatment scheme. METHODS: A total of 350 consecutive invasive breast carcinoma biopsies were assessed and compared with surgical specimens in Institut Curie, Paris, France. Clinical, radiological and pathological data were recorded. RESULTS: Histological grade concordance rate in the HR+/HER2− group was 75%. A grade underestimation was mainly due to mitotic index misgrading (23%). Large tumours (P<0.05), premenopausal patients (P=0.005) and non-ultrasound-guided biopsies (P=0.04) were risk factors for misgrading. The highest discordance was found in tumours that required chemotherapy (39%, P<0.05), and it was related to an underestimation of histological grade on core biopsies (94%). CONCLUSIONS: Histological grade in HR+/HER2− group is important to identify patients with poor prognosis and start a systemic therapy. Histological grade discordance was correlated with an underestimation of mitotic index and factors probably associated with intratumor heterogeneity (premenopausal status, tumour size and the type of core biopsy performed). But such discordance did not appear to modify the therapeutic decision, because systemic treatment decision-making also integrates other variables. Determining histological grade in core biopsy can be especially important in HR-positive/HER2-negative subgroup where it identifies patients at high risk and is a strong determinant of the treatment scheme.