Preoperative Radiotherapy (Preop-RT) Improves Pathological Complete Response Rates in Partial Responders (PR) to Primary Systemic Chemotherapy (PST) in Locally Advanced Breast Cancers (LABC).

Introduction: Preoperative radiotherapy (preop-RT) can be used as one strategy to improve pathological complete response rates in locally advanced breast cancer. Hence, we conducted a pilot study of preop-RT in partial responders to primary systemic chemotherapy (PST). Methods: Standard PST comprising of four cycles of Adriamycin/cyclophosphamide followed by four cycles of taxanes (along with trastuzumab in Her2-neu enriched) was initiated. After two cycles of taxanes, partial responders (PRs) were enrolled onto preop-RT (40 Gy/15#/3 weeks to whole breast followed by boost dose of 10 Gy/4#/1 week to gross tumor with 5 mm margin [clinical target volume] and 10 mm margin [planning target volume] by three-dimensional conformal radiation therapy. Field-in-field technique was used whenever the need to correct dose heterogeneity arose. The remaining two cycles of taxanes were completed 3 weeks after the completion of RT. Surgical intervention was initiated 6 weeks after the completion of PST. The intention of such a strategy was to keep an interval of 12 weeks between completion of RT and surgery to achieve maximum downstaging. The primary endpoint was pathological complete response rate (ypCR). Results: Twenty-one women were enrolled (median age 47 years, 35% premenopausal, 50% upper outer quadrant, 65% T4, 85% node positive, 40% luminal A, 10% luminal B, 15% Her-2-neu enriched, and 35% triple-negative breast cancer [TNBC]). Twenty-eight percent underwent breast conservation and the rest modified radical mastectomy ( Conclusion: This pilot study reveals encouraging results in high-risk subsets and this potential of preop-RT should be explored further in larger studies.