Abstract PO5-03-09: Concurrent versus sequential use of adjuvant capecitabine and radiation in patients with triple-negative breast cancer with residual disease: A retrospective review

Abstract Background: The CREATE-X trial demonstrated benefit of adjuvant capecitabine for patients with triple-negative breast cancer (TNBC) with residual disease after neoadjuvant chemotherapy and surgery. In clinical practice however, physician discretion determines the sequence of capecitabine relative to radiation therapy (RT), as well as the treatment dose. Therefore, our study aimed to assess the treatment patterns and tolerance of capecitabine and RT in patients with residual TNBC at our institution after publication of the CREATE-X study. Methods: This was a retrospective IRB-approved study that included patients with TNBC who had residual disease following neoadjuvant chemotherapy and surgery and received both adjuvant loco-regional RT and capecitabine at our institution between July 1, 2017 and June 30, 2021. Patient characteristics and treatment regimens were abstracted from medical charts. For this study, we defined optimally-delivered capecitabine to be a starting dose of 1250 mg/m2 twice per day on days 1-14 every 3 weeks as per the CREATE-X trial, and all planned cycles completed without dose reductions or discontinuation. RT was defined as optimally delivered when patients completed the prescribed dose without a treatment break of > 1 week or discontinuation of planned RT. We used descriptive statistics to report our observations. Results: Thirty-four patients met our eligibility criteria. The median age at diagnosis was 56 years (range: 30-77 years) and the median follow up time was 48 months. Of the 27 patients who received sequential RT and capecitabine, the median starting dose of capecitabine was 1000 mg/m2. Of the 7 patients who received concomitant RT and capecitabine, the median starting dose during RT was 800 mg/m2; after completion of RT, patients completed 6 additional cycles of capecitabine at a median dose of 1000 mg/m2. We observed a greater residual breast tumor burden in patients prescribed concomitant RT and capecitabine; 71.4% were ypT2/T3 compared to only 18.5% ypT2/T3 in sequentially treated patients (OR 11.0; 95% CI, 1.64 to 73.97; p=0.05). There was no significant difference in the positive lymph node status between the 2 groups (42.9% and 40.7%, respectively). A median RT dose of 50 Gy in 25 fractions was delivered in both schedules. No patients discontinued RT due to intolerance. In the 27 sequentially treated patients, the majority (73%) received RT before capecitabine. Among these, 14 patients (51.9%) required a dose reduction and 6 patients (22.2%) discontinued capecitabine due to intolerance. Of the 7 patients receiving concomitant RT and capecitabine, 2 patients (28.5%) discontinued capecitabine due to intolerance (one during RT and one following completion of RT). The concomitant RT and capecitabine regimen was not associated with higher odds of prematurely discontinuing capecitabine compared to the sequential schedule (OR 1.15; 95% CI, 0.18 to 7.34). Conclusion: In this study, most patients received a sequential schedule and those with a higher residual disease burden were more likely to be prescribed concomitant RT and capecitabine. The starting dose of capecitabine in both schedules was lower than the starting dose in the CREATE X trial but consistent with the practice standard in the US. Our early experience did not demonstrate any signal to suggest a difference in the tolerance of capecitabine administered sequentially or concurrently. Further studies are needed to evaluate the optimal sequence of RT and capecitabine in the adjuvant setting. Citation Format: Catherine Yu, Alaina Kessler, Theresa Shao, Sarah Cate, Paula Klein, Manjeet Chadha. Concurrent versus sequential use of adjuvant capecitabine and radiation in patients with triple-negative breast cancer with residual disease: A retrospective review [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 PO5-03-09.