Fatigue following radiotherapy of low-risk early breast cancer - a randomized controlled trial of intraoperative electron radiotherapy versus standard hypofractionated whole-breast radiotherapy: the COSMOPOLITAN trial (NCT03838419).

<bold>Background: </bold>Fatigue is one of the most common and distressing side-effects of breast cancer radiotherapy. According to current guidelines, accelerated partial breast irradiation (APBI) may be considered as an alternative treatment option for women with early-stage low-risk breast cancer. One method for APBI is single-dose intraoperative radiotherapy (IORT) applied directly to the tumor bed during breast conserving surgery (BCS). The COSMOPOLITAN trial therefore aims to analyze the intensity of fatigue following single-shot IORT with electrons (IOERT) compared to conventional hypofractionated whole breast irradiation (WBI) in low risk early breast cancer patients.<bold>Methods: </bold>This trial is conducted as a multicenter, prospective, randomized, two-arm phase II study comparing the intensity of fatigue in early-stage breast cancer (cT1cN0cM0, tumor size < 2,5 cm, ER pos. Her2neu neg., age > 50 years) treated either with WBI or APBI after BCS. Secondary outcomes investigated are tumor control, overall survival (OS), disease-free survival (DFS), acute and chronic toxicity, quality of life (QoL) and cosmesis. A total of 202 patients will be randomized into two arms: Patients in arm A will receive WBI (40.05 Gy, 15 fractions) after surgical resection, while patients in arm B will receive IOERT (21 Gy to the 90%-isodose) during BCS. Fatigue will be assessed 12 weeks post surgery with the help of the Functional Assessment of Chronic Illness Therapy (FACIT) Fatigue Scale.<bold>Discussion: </bold>The present trial aims to evaluate treatment response to compare single-shot intraoperative electron APBI to conventional WBI following BCS in early-stage low risk breast cancer patients. Fatigue is selected as the primary, patient-reported endpoint due its major clinical relevance.<bold>Trial Registration: </bold>The study is prospectively registered on February 12th, 2019: Clinicaltrials.gov, NCT03838419. "Intraoperative Electron Radiotherapy for Low-risk Early Breast Cancer (COSMOPOLITAN)".<bold>Study Status: </bold>Ongoing study. Start of recruitment was December 2019. [ABSTRACT FROM AUTHOR]