Abstract OT1-2-02: SHARE. A French multiceter phase III trial comparing accelerated partial irradiation (APBI) versus standard or hypofractionated whole breast irradiation in low risk of local recurrence breast cancer

Introuction: The six worldwilde ongoing APBI phase III trials are characterized by a significant heterogeneity regarding inclusion criteria and stratifications. One non-inferiority trial (SHARE) is currently ongoing in France. SHARE Trial design: SHARE will randomize 2800 patients in 3 arms: standard (Arm A; 6.5 weeks) versus hypofractionated (Arm B; 3 weeks) versus APBI (Arm C; 1 week) using only 3D conformal radiotherapy (3D CRT). In this trial high quality and homogeneous criteria in surgery, pathology and RT for the 3 arms is planed. Primary objective: To estimate and compare the rates of local recurrences between the experimental and control arms. Inclusion criteria Post menopausal women aged ≥ 50y (stratification: Menopausal status confirmed since ≥ 12 months (Clinically and/or biologically) No previous ipsilateral breast and/or mediastinal irradiation Pathologic confirmation of invasive carcinoma (all types of invasive carcinomas) Unifocal tumor confirmed on the pathologic specimen Pathologic tumor size of the carcinoma ≤ 2cm (including the in situ component) All pathologic grades (stratification: HER2/triple negative vs others) Clear lateral margins confirmed on the final pathology report. The minimal size from the invasive and in situ disease should be 2 mm (≥ 2mm) pN0 (i+/−) (stratification: pN0 vs pN(i+)) Chemotherapy and trastuzumab are not allowed - RT should be started ≥ 4weeks and ≤ 12 weeks after surgery (including the date of second excision for close or involved margins) Clips in the tumor bed placed during surgery (4 to 5 clips) Treatment Arm A 3D CRT should be started within 12 weeks after the last surgery. A total of 50 Gy is delivered in 25 fractions, one fraction of 2 Gy per day, 5 days a week. In this arm, the boost of 10 to 16 Gy is delivered in 5 to 8 fractions. Dose prescription (arm B) The main point is that in both schedules the total dose is delivered in 3 weeks: – The Canadian schedule described by Whelan et al. delivers 42.5 Gy in 16 fractions (2.65Gy/fraction, 5 fractions/week). – The UK schedule, reported in START B trial delivers 40 Gy in 15 fractions (2.66 Gy/ fraction, 5 fractions/week). Nodal and boost RT is not allowed. Arm C 3D CRT should be started within 12 weeks after the last surgery. Intensity modulated RT (IMRT) and brachytherpayare not allowed. A total dose of 40 Gy in 10 fractions over 1 week (4Gy per fraction twice a day with minimal delay of 6h). Conclusion: In summary, the French trial will allow: – Selected patients according to age and low risk of local recurrence parameters. – To evaluate in a subgroup of patients (4 to 5 centers), the impact of magnetic resonance imaging (MRI) for patient selection and the rate of occult disease (multifocality) not detected by standard imaging evaluation which is considered as an exclusion criteria. – To determine APBI parameters adapted to the surgical procedure in the tumor bed remodeling setting. – To determine homogeneous criteria for the surgical procedure, minimal requirements and optimal criteria that have to be mentioned in the final pathology report in all 3 arms of the study. – To test hypofractionation using 3 weeks-schedules as compared to APBI Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr OT1-2-02.