Effect of neoadjuvant chemotherapy on breast cancer phenotype, ER/PR and HER2 expression - Implications for the practising oncologist.

Abstract Purpose To assess the effect of neoadjuvant chemotherapy (NACT) on breast cancer characteristics, hormone receptors and human epidermal growth factor receptor 2 (HER2) expression and whether testing should be repeated on residual tumours. Material and methods Patients with primary operable breast cancer who received NACT at a single United Kingdom tertiary referral centre were included. Tumour type, grade (including details of mitotic grade, tubule formation and pleomorphism), oestrogen receptor (ER), progesterone receptor (PR) and HER2 status were compared between pre-treatment and post-treatment residual samples using tissue microarrays. A control group of paired core and excision tumours from patients who did not receive NACT was also assessed. Results Two hundred forty-six cases and 113 controls were included. Pathological complete response (path CR) was achieved in 21.5% of patients. In those patients failing to achieve a path CR, a change in the histological type was noted in 29 out of 178 cases (16.3%, p Conclusion Significant changes in tumour morphology, grade, hormone receptors and HER2 status occur following NACT. We recommend testing on residual invasive carcinoma. A switch from negative to positive status warrants offering endocrine/trastuzumab-based therapy to this group of patients.