Abstract P2-16-11: Impact of progesterone receptor status on response to neoadjuvant chemotherapy in oestrogen receptor positive breast cancer patients

Introduction Breast cancer patients respond differently to neoadjuvant chemotherapy (NAC) based on hormone receptor subtype. Oestrogen receptor positive/Her-2 receptor negative (ER+HER-) patients respond poorest but the effect of progesterone receptor (PR) status on response within this group has not been elucidated. The aim of this study was to assess the impact of PR status on response to NAC in ER+HER- breast cancer patients. Methods All patients receiving NAC over a seven-year period (2011-2017) were retrospectively identified from a prospectively maintained database within a specialised breast referral unit. Clinicopathological details were collated for all patients found to be ER+HER-. Primary outcomes including breast complete pathological response (PCR) rate and axillary PCR rate were compared between patients found to be progesterone receptor positive and negative. Secondary outcomes including grade and presence of lymphovascular invasion were also assessed. Results 206 patients were identified (151 in the ER+PR+HER- group and 55 in the ER+PR-HER- group). When compared with the PR+ group, patients found to be PR negative were more likely to achieve a breast PCR (3.3% vs 25.4%; Chi Square test; p=0.001), which was confirmed on multivariate analysis (p=0.001).In patients who were initially node positive, PR negativity was associated with a higher rate of axillary nodal PCR compared to those found to be PR positive(12.2% vs 25.5%; Chi Square test; p=0.04). ER+PR-HER- patients were more likely to have higher grade tumours but not LVI. Conclusion Over a quarter of ER+HER- patients who are PR negative will have a complete pathological response to NAC in the breast and axilla. Such patients should be considered for NAC at diagnosis. Citation Format: Michael R Boland, Eanna J Ryan, Timothy Nugent, Darina Gilroy, John Kennedy, Dhaffir Alazawi, Terence J Boyle, Elizabeth M Connolly. Impact of progesterone receptor status on response to neoadjuvant chemotherapy in oestrogen receptor positive breast cancer patients [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-16-11.