Abstract PO5-17-08: Real world outcomes of neoadjuvant chemotherapy in ER-positive/PR-positive, HER2-negative breast cancer

Abstract Background: Neoadjuvant chemotherapy is utilized to downstage locally-advanced estrogen receptor-positive (ER+)/progesterone receptor-positive (PR+), HER2-negative breast cancer despite modest pathological complete response (pCR) rates. The two most commonly utilized regimens include docetaxel plus cyclophosphamide (TC) or dose-dense doxorubicin and cyclophosphamide followed by paclitaxel (ddAC-T). Given few head-to-head comparisons of neoadjuvant TC with ddAC-T in this population, we performed a real world data analysis. Methods: 148 patients with ER+/PR+, HER2-negative breast cancer were included in the analysis. The patients were divided into two groups based on the neoadjuvant chemotherapy regimen used (TC vs ddAC-T) and the clinical responses to chemotherapy were categorized as complete, partial, no response/stable, or progressive disease. We examined the differences or associations in demographics, clinical characteristics, overall survival (OS), and invasive disease-free survival (IDFS) between TC and ddAC-T neoadjuvant chemotherapy. pCR was defined as the absence of invasive carcinoma in breast and lymph nodes (ypT0/ypTis and ypN0). Partial response was defined as a decrease in either or both T and/or N stage, compared to pre-treatment evaluation; no response was defined as no change in either T or N categories; and progressive disease was defined as an increase in either the T or N staging at time of pathologic evaluation. Results: The median age of participants was 55 years (range 28-78 years). 67% had clinical stage II disease, while 26% had stage III. 130 participants received neoadjuvant ddAC-T while 18 participants received TC. The ddAC-T group had 7% patients who achieved a pCR and 37% with a partial response, compared to the TC group with 0% of patients with a pCR and 33% with a partial response. The TC group had a higher rate of progressive disease, compared to the ddAC-T group (67% versus 20%). On univariate analysis, the choice of neoadjuvant chemotherapy was not predictive of pathologic response (p = 0.3864). As expected, premenopausal status was associated with a higher likelihood of a pathologic response with an odds ratio of 2.917 (95% CI: 1.465-5.809). On multivariate analysis, chemotherapy regimen was not predictive of pathologic response (p = 0.6047), after controlling the effects of age and menopausal status. No significant difference was noted in OS or IDFS at 24 and 48 months between the ddAC-T and TC groups. On multivariate analysis, controlling for BMI, ER, PR, race, and ECOG performance status, the choice of chemotherapy was not predictive of IDFS. Non-white participants appeared to have inferior IDFS (HR = 2.956, 95% CI: 1.208, 7.238, p-value = 0.0177). Conclusion: In this single-center retrospective analysis, we show real world outcomes of the use of neoadjuvant chemotherapy regimens among patients with ER+/PR+, HER2-negative breast cancer. Both ddAC-T and TC had low pCR rates, 5.98% and 0%, respectively. However, there was no statistical difference between IDFS or OS when comparing the two chemotherapy regimens. More data are needed to optimize neoadjuvant treatment in this patient population and to determine whether anthracyclines can be avoided. Table. Pathologic responses The results (summarized by odds ratio (OR) and its 95% CI) from logistic regression on the pathological responses (complete and partial). Citation Format: Matthew Kurian, Marcus Trybula, Kanchi Patell, Gregory Guzik, Seunghee Margevicius, Pingfu Fu, Alberto Montero, James Martin. Real world outcomes of neoadjuvant chemotherapy in ER-positive/PR-positive, HER2-negative breast cancer abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-17-08.