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Low human epidermal growth factor receptor 2 (HER2) expression is emerging as an actionable biomarker for the treatment of breast cancer (BC) with novel anti-HER2 drugs. However, the evolution of this biomarker during the course of disease is still poorly characterised, and controversial data exist on its prognostic implications. We reviewed data of patients with HER2-negative BC according to the latest ASCO/CAP guidelines referred between January 2014 and December 2020. We grouped patients based on the immunohistochemistry (IHC) expression of HER2, HER2-zero (IHC 0) and HER2-low subgroup (IHC 1+ or 2+/ISH-negative) and evaluated the evolution of HER2 expression between the primary tumour and the first biopsy collected in the advanced setting. Disease-free survival, overall survival and progression-free survival were compared between patients with HER2-zero and HER2-low expression on the primary tumour. 232 patients were included in the analysis. Among the overall population, there was a relevant discordance in HER2 expression between the primary tumour and the matched biopsy (K = 0.33, 95%CI 0.21–0.44): 44% of the HER2-zero primary tumour showed an increased HER2 score on biopsy, and 22% of the HER2-low primary tumours turned into HER2-IHC 0. The findings in the sub-populations of hormone-receptors positive (K = 0.32, 95%CI 0.19–0.45) and triple-negative tumours (K = 0.18, 95%CI -0.09-0.46) were consistent with the primary analysis. No difference in survival outcomes was observed between HER2-low and HER2-zero primary tumours. HER2-low expression is dynamic in BC and may be enriched in the advanced-stage setting. No prognostic significance was demonstrated for HER2-low expression. • HER2-low expression is emerging as an actionable biomarker in breast cancer. • HER2 IHC score increased from primary to metastatic tumour in 44% of the patients. • HER2-low to HER2-zero evolution was observed in 22% of the patients. • HER2-low expression is dynamic and may be enriched in the advanced-stage setting. [ABSTRACT FROM AUTHOR]

Abstract: Premises: Sentinel node biopsy (SNB) in patients with breast carcinoma accurately predicts the axillary node status. However, in some 4–7% of patients with negative sentinel nodes, the remaining axillary nodes harbour cancer cells. Objective: Our purpose was the long-term observation of a large number of patients who did not receive axillary dissection after a negative sentinel node biopsy, in order to evaluate the incidence of overt axillary metastases. Methods: Patients (3548) treated from 1996 to 2004, with negative sentinel nodes not submitted to axillary dissection, were followed up to 11 years with a median follow-up of 48 months. Results: Three hundred and sixteen unfavourable events occurred among the 3548 patients, 196 of which (5.5%) related to primary breast carcinoma. Thirty one cases of overt axillary metastases were found (0.9%): they received total axillary dissection and 27 of them are at present alive and well. The 5-year overall survival rate of the whole series was 98%. Conclusions: Patients with negative sentinel node biopsy not submitted to axillary dissection show, at follow-up, a rate of overt axillary metastases lower than expected. [Copyright &y& Elsevier]