Concurrent use of capecitabine with radiation therapy and survival in breast cancer (BC) after neoadjuvant chemotherapy.

e12117 Background: Capecitabine has been studied as a radiosensitizer in rectal cancer, but its role in BC is unclear. Our study seeks to examine the association of concurrent capecitabine/radiation therapy (RT) on survival in women with BC and residual disease after neoadjuvant chemotherapy (NAC). Methods: In a retrospective study of women with stage I-III BC who received Adriamycin/Taxane-based NAC from 2010-2016, we identified 21 women administered concurrent capecitabine/RT. To assess differences in survival, we selected a clinical control cohort (n = 64) based on criteria used to select patients for capecitabine/RT including pathological stage II/III disease and non-HER2+ tumor subtype. We also created a matched cohort (2:1), matching on tumor subtype, pathological stage, and age ( < 50 or 50+ years). Differences in progression-free survival (PFS), using STEEP criteria, and overall survival (OS), using all-cause mortality, between those who received capecitabine/RT and controls were assessed. Results: Of the 21 women who received capecitabine/RT, the majority were 50+ years (n = 12), pathological stage III (n = 15), and hormone receptor positive/HER2 negative BC (n = 20). Compared with clinical controls, women who received capecitabine/RT had larger disease (p = 0.041) and a higher pathological stage (p = 0.067), but there were no other differences. In those receiving capecitabine/RT, there were 9 recurrences (3 local, 6 distant) compared with 14 recurrences (4 local, 10 distant) in the clinical controls and 10 recurrences (all distant) in the matched controls. In multivariate models, capecitabine/RT was associated with worse PFS (HR 3.04 95% CI 1.24-7.43 p = 0.015) and OS (HR 4.29 95% CI 1.45- 12.6 p = 0.008), after adjusting for clinical size and pathologic stage. In the 2:1 matched cohort, capecitabine/RT was also associated with worse PFS (HR 2.96 95% CI 1.20-7.29 p = 0.018) and OS (HR 5.61 95% CI 1.76-17.9 p = 0.004). Conclusions: Capecitabine/RT after NAC is associated with worse PFS and OS using two control populations, suggesting capecitabine/RT should be discouraged in BC.