Abstract PS1-08-04: Acute skin toxicity with ultra-hypofractionated whole breast radiation therapy after lumpectomy for breast cancer: a single institutional experience

Abstract Intro: Randomized control trials have shown that adjuvant breast radiation therapy (RT) reduces local recurrence after lumpectomy for breast cancer. The most common adverse effect of RT is radiation dermatitis and is seen in 90% of patients. Hypofractionated (HF) dosing leads to a lower degree of acute radiodermatitis and better patient outcomes compared to conventional radiation, and we aimed to see if ultra-hypofractioned radiation therapy (UHF-RT) continues this trend.1 The current standard of care has changed from treatment over 5 - 6 weeks to a more accelerated HF approach typically over 3 - 4 weeks. Based on the FAST-FORWARD trial, a 5-fraction course of UHF-RT is evolving into a new standard of care to significantly reduce costs and increase access, compliance, and adoption of adjuvant radiotherapy.2 The purpose of this study is to review the acute skin toxicity in a cohort of patients who have undergone UHF-RT. Methods: We conducted a retrospective chart review of 20 patients who have undergone post-lumpectomy UHF-RT. All 20 patients received 2600 cGy to the whole breast in 5 fractions, and 8 of those patients received a single fraction boost dose of 520 cGy. Radiation plans were delivered as field in field tangential plans using 6 MV photons with a dose homogeneity within 105%. We graded skin toxicities G0 to G5, according to NCI-CTCAE criteria, at 1-month and 6-months post-treatment based on follow-up examinations. Results: All patients were females between the ages of 50 and 95 years old. 85% were ER+, 85% were PR+, and 5% were HER2+. The Ki-67 percentages ranged from 10% to 70%. There were no known ATM mutations in our cohort. T stages were as follows: Tis (20%), T1 (65%), and T2 (15%). Lymph node status showed: N0 (85%), N1 (10%), and NX (5%). The radiation fields treated breast only in 95% (n=19) and breast and axillary nodes in 5% (n=1). In addition to UHF-RT, 10% (n=2) of patients received chemotherapy and 80% (n=16) received anti-estrogen therapy. Skin toxicity at 1 month was G0 for 4/20 and G1 for 16/20 patients. For patients with a minimum 6-month follow-up (n=16), skin toxicity observed was G0 for 11/16 and G1 for 5/16 patients. Of the 20 patients who received UHF-RT, 40% (n=8) received a boost dose. At 1-month, 8/8 of boost dose patients were G1. Boost dose patients with a 6-month follow-up (n=6) showed G1 for 4/6 and G0 for 2/6. None of the 20 patients developed worse than a G2 skin toxicity, and all patients completed their treatment as planned, with no breaks in treatment. Conclusion: UHF-RT significantly reduces the costs of treatment and therefore can improve patient compliance and access. This study shows an additional benefit of decreased skin toxicity severity after UHF-RT, even with a boost dose administered, compared to HF radiation protocol. Though these results are promising, further follow-up is necessary to confirm these findings and to assess potential long-term effects (> 6 months) of UHF-RT after lumpectomy for breast cancer. References: 1. Borm, K. J., et. al. (2021). A Comprehensive Prospective Comparison of Acute Skin Toxicity after Hypofractionated and Normofractionated Radiation Therapy in Breast Cancer. Cancers, 13(22), 5826. https://doi.org/10.3390/cancers13225826. 2. Brunt, A. M., et al. (2020). Hypofractionated breast radiotherapy for 1 week versus 3 weeks (FAST-Forward): 5-year efficacy and late normal tissue effects results from a multicentre, non-inferiority, randomised, phase 3 trial. The Lancet, 395(10237), 1613-1626. https://doi.org/10.1016/s0140-6736(20)30932-6 Citation Format: S. Juang, J. Neiswander, A. Ragupathi, D. Zhang, M. M. Plummer, R. Rajasree, E. Obedian. Acute skin toxicity with ultra-hypofractionated whole breast radiation therapy after lumpectomy for breast cancer: a single institutional experience [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS1-08-04.