Practice patterns impacting relative dose intensity of adjuvant capecitabine among triple negative breast cancer patients with residual disease following neoadjuvant chemotherapy

Background: This study aims to identify real-world practice pattern factors in capecitabine prescribing and assess which factors lead to higher relative dose intensity (RDI) to help address the variability in dosing strategies that limits the ability to assess the real-world effectiveness of adjuvant capecitabine. Methods: This institutional retrospective study involved patients diagnosed with triple negative breast cancer from 1/1/2016 to 12/31/2023 who had residual disease following neoadjuvant chemotherapy and received ≥1 dose of adjuvant capecitabine. Our objective was to examine factors that influence the achievement of an RDI >66%, with standard dosing based on a total of 8 cycles of capecitabine over 21-day cycles. Factors included radiation therapy, dose reductions, prescribing schedule, age, race, tumor grade, nodal status, tumor size, residual cancer burden, lymphovascular invasion, and neoadjuvant pembrolizumab & carboplatin. We also examined whether RDI impacts invasive disease-free survival (iDFS) and overall survival (OS) using pre-defined percentiles (0-66%, 67-92%, & 93-100%). Results: Of the 83 total patients, 45 were RDI≤66, 29 were RDI>67-92, & 9 were RDI≥92-100. Among all clinicopathologic factors listed above, only the use of a 7-day prescribing schedule for capecitabine (28-day cycle) had a meaningful reduction on one's ability to reach an RDI of >66% (p=0.0234). When examining univariate iDFS, no statistically significant difference was noted between RDI percentiles (p=0.667) but a trend towards improved iDFS was noted among higher RDI groups. The 5-year iDFS was 78.4% for RDI≤66, 77.9% for RDI>67-92, & 88.9% for RDI>93-100. Similarly for OS, no statistically significant difference was noted between RDI percentiles (p=0.395), but a trend towards improved OS was noted when RDI exceeded 66%. The 5-year OS was 82.1% for RDI≤66, 92.7% for RDI>67-92, & 88.9% for RDI>92-100. Conclusion: Real world practice patterns can differ, but the implementation of weekly capecitabine dosing frequency has been shown in this study to significantly influence the ability to achieve higher RDI values. While no statistical difference in iDFS or OS was noted, a trend towards worsening outcomes was recorded for those with an RDI≤66%.