Abstract SS1-06: Racial disparities in pathological complete response among breast cancer patients receiving neoadjuvant chemotherapy

Background: With the increasing use of neoadjuvant chemotherapy in breast cancer patients, it is important to better understand how host factors interact with tumor characteristics to determine response to neoadjuvant chemotherapy. Pathological complete response (pCR) is a strong surrogate for long term survival in certain subtypes of breast cancer. Racial disparities in breast cancer survival have been well documented, but few studies have been conducted to examine the extent of racial disparities in pCR after neoadjuvant chemotherapy. Method: We established a cohort of patients with breast cancer treated at an academic medical center in the ethnically diverse City of Chicago — the Chicago Multiethnic Epidemiologic Breast Cancer cohort (ChiMEC). Among patients who received neoadjuvant chemotherapy, we examined whether racial disparity existed in the rate of pCR, defined as ypT0/isypN0. Multivariable logistic regression models were used to estimate the odds ratios (ORs) of black relative to white patients, adjusting for clinical tumor stage and molecular subtype. We also explored whether there were racial difference in treatment characteristics, including days from diagnosis to the first neoadjuvant chemotherapy and dosage of 7 most commonly used drugs (Carboplatin, Cyclophosphamide, Docetaxel, Doxorubicin, Paclitaxel, Trastuzumab and Pertuzumab) using Wilcoxon rank-sum tests. Results: The study consisted of 595 stage I-III breast cancer patients who received neoadjuvant chemotherapy (51% Whites and 40% Blacks). Among them, 32.5% of the White patients achieved pCR while only 23.9% of the Black patients achieved pCR (Table). After adjusting for tumor subtype and clinical stage, Black patients still had a significantly lower odds of achieving pCR compared to Whites (OR=0.67, 95% CI: 0.44-1.00). The racial difference in pCR rates existed in all four molecular subtypes, though most pronounced in the HR-/HER2+ subgroup (OR=0.35, 95% CI: 0.13-0.97). Further adjusting for time from diagnosis to first chemotherapy reduced the racial difference (OR=0.76, 95% CI: 0.50-1.15), suggesting that some of this racial disparity could be explained by delay in treatment initiation. This hypothesis is also supported by the observation that the largest racial difference in treatment initiation was in the HR-/HER2+ subgroup, with White patients taking an average of 30.9 days to get their first chemotherapy after diagnosis while Black patients taking an average of 45.4 days (P = 0.019). In addition, the study found that Black patients received significantly less cycles of Cyclophosphamide and Doxorubicin (i.e., the AC regimen) than White patients (P = 0.024). Conclusion: Our study showed that Black patients had a lower pCR rate after neoadjuvant chemotherapy, and this racial disparity was largest among HR-/HER2+ patients. Although delayed initiation of treatment may partially contribute to this racial disparity, treatment differences in this single institution study are relatively small so most of racial disparity in response to neoadjuvant therapy could be due to biological difference beyond subtypes. Host and tumor characteristic that modulate response to therapy in diverse populations deserve further exploration to optimize design of innovative clinical trials and reduce disparities in clinical outcomes. Citation Format: Fangyuan Zhao, Meghan Steiner, Abiola Ibraheem, Gini Fleming, Nora Jaskowiak, Rita Nanda, Olufunmilayo I. Olopade, Dezheng Huo. Racial disparities in pathological complete response among breast cancer patients receiving neoadjuvant chemotherapy [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr SS1-06.