Neoadjuvant Chemotherapy Exerts Selection Pressure Towards Luminal Phenotype Breast Cancer.

Background: Breast cancer (BC) phenotype after neoadjuvant chemotherapy (NAC) has not been extensively described and few data exist on whether expression of the primary tumor hormone receptors, HER2 and Ki-67 changes as a result of chemotherapy.

Materials And Methods: We analyzed specimens from all BC patients treated with anthracycline/taxane-based NAC at our Institution between January 2010 and March 2015 (n = 325). The expression of estrogen receptor (ER), progesterone receptor (PR), HER2 and Ki-67 was determined in pre- and post-NAC specimens. McNemar's test was used to compare paired proportions.

Results: Among patients with residual disease after NAC, basal phenotype was luminal A, luminal B, HER2 positive and triple negative in 44, 111, 74 and 27 cases, respectively. PR-positive tumors decreased from 68.0% in the initial biopsy sample to 61.7% in the surgical specimen (p = 0.024). A Ki-67 of < 20% increased from 23.6% to 45% (p < 0.001). ER expression changed from positive to negative in 5% and from negative to positive in 16.7% of cases. Overall, 30% of cases underwent subtype changes, 79% of them towards luminal differentiation.

Conclusions: The switch towards luminal phenotype suggests some kind of endocrine effect of NAC. Our findings raise renewed interest in combinatorial cytotoxic chemotherapy with concomitant or rather sequential endocrine therapy, either alone or with targeted agents.