Effect of addition of adjuvant paclitaxel on radiotherapy delivery and locoregional control of node-positive breast cancer: cancer and leukemia group B 9344.

Purpose: We compared radiotherapy (RT) delivery and locoregional control in patients with node-positive breast cancer randomly assigned on Cancer and Leukemia Group B 9344 to receive adjuvant doxorubicin/cyclophosphamide (AC) with patients assigned to receive AC followed by paclitaxel (AC+T).
Methods: Eligible patients were randomly assigned to receive adjuvant AC versus AC+T chemotherapy. RT was required if breast-conserving surgery was performed but was elective after mastectomy. Information about RT delivery was retrospectively collected. Cumulative incidence of locoregional recurrence (LRR), use of elective RT, and RT delivery were compared between treatment arms.
Results: For patients treated with breast-conserving surgery and RT, the 5-year cumulative incidence of isolated LRR was 9.7% in the AC arm and 3.7% in the AC+T arm (P = .04) and of LRR as any component of failure was 12.9% versus 6.1%, respectively (P = .04). Although LRR rates in patients who did not receive postmastectomy RT were lower in the AC+T arm, the difference was not statistically significant. Despite the lack of protocol guidelines, RT use did not differ between arms, nor did RT dose, treatment interruption, or completion.
Conclusion: Despite the delay to RT during additional chemotherapy, adjuvant AC+T afforded better local control than AC alone in patients treated with breast-conserving therapy. Addition of paclitaxel did not adversely affect delivery or ability to tolerate RT, as indicated by similar rates of completion of timely, full-dose RT between arms.