Impact of sequence order of anthracyclines and taxanes in neoadjuvant chemotherapy for breast cancer: Results from a prospective institutional database.

e12619 Background: There has been growing interest in the optimal sequencing of anthracyclines and taxanes in neoadjuvant chemotherapy (NACT) for breast cancer. However, data comparing efficacy of administering taxanes prior to anthracyclines as opposed to the opposite sequence remains limited and inconsistent. The objective of our study was to assess the impact of sequence order on pathologic and clinical outcomes in a real-world setting. Methods: A prospective institutional database was analyzed to identify all HER2-negative breast cancer patients treated with NACT from 2012 to 2019. Rates of pathologic complete response (pCR), down-staging, and breast-conserving surgery were compared between patients who received anthracyclines followed by taxanes (AC-T) to those who received taxanes followed by anthracyclines (T-AC). Chi-square and independent sample non-parametric tests were used to test for associations between variables and outcomes. Results: Of the 270 patients who met eligibility criteria, 175 (65%) received AC-T and 95 (35%) received T-AC. Median age was 55 (IQR 24-86). Overall, 83% of patients had stage IIB or greater tumors, 40% had grade 3 histology, and 36% had triple-negative disease. Characteristics were balanced between the AC-T and T-AC groups (all p < 0.05). Median duration of treatment with NACT was 102 days (IQR 29-203). Rates of pCR (19% vs 21%, p = 0.750), down-staging (68% vs 61%, p = 0.188), and conversion to breast-conserving surgery (26% vs 20%, p = 0.314) were similar for AC-T vs T-AC, respectively. pCR was higher in triple-negative compared to hormone-positive cases (33% vs 13%, p < 0.001). Conclusions: In this small population-based cohort, sequence order of anthracyclines and taxanes did not demonstrate statistically significant differences in evaluated outcomes from NACT for breast cancer. This supports the current variation in prescribing practice and highlights the need for further studies in this area.