Abstract OT1-09-01: Phase II trial assessing accuracy of tumor bed biopsies in predicting pathologic response in patients with clinical/radiological complete response after neoadjuvant chemotherapy in order to explore the feasibility of breast-conserving surgery without surgery: NRG Oncology BR005

The increased use of neoadjuvant chemotherapy (NCT) has enabled higher rates of breast-conserving surgery (BCS) as well as provided prognostic information for women with breast cancer. High pathological complete response (pCR) rates question the requirement for surgery, with its attendant morbidity. In order to avoid surgery, the ability to predict pCR prior to it must be very high. Trimodality imaging alone is inadequate to predict pCR prior to surgery. We hypothesize that performing core-needle biopsy (bx) of the tumor bed in addition to trimodality imaging in patients (pts) having had a clinical complete response (cCR) will increase the ability to predict pCR. Utilizing predetermined imaging response criteria of complete or near-complete response coupled with a stereotactic core-needle bx of the tumor bed, BR005 aims to determine the predictive value of imaging followed by tumor bed bx for pCR and demonstrate its reproducibility across a multi-institutional setting. Methods: 175 pts with operable focal or multifocal (T1-T3), stage II/IIIA invasive ductal carcinoma (all receptor subtypes) will be entered. Pts must have completed a minimum of 8 wks of standard NCT and achieved a complete or near-complete radiologic tumor response on breast imaging with mammogram, ultrasound, and MRI, and undergo BCS. Following cCR and prior to surgery, pts will undergo a stereotactic-vacuum-assisted breast bx with clip placement. The primary endpoint is the proportion of pts with post-NCT neg image-directed bx who have a pCR. Residual cancer burden scores and core bx pathology will be collected along with trimodality imaging data. Evaluation after 135 pts will allow for the possibility of early termination of the study. Results will provide the first step toward a paradigm change in the treatment of breast cancer, enabling a study to assess the criteria for successful avoidance of surgery in pts with high response rates to NCT. Accrual as of 6-15-18: 39 (22.3%). Support: U10CA180868, -180822, UG1CA189867. Citation Format: Basik M, Costantino JP, De Los Santos JF, Umphrey HR, Julian TB, Mamounas EP, White JR, Lucas PC, Wagner JL, Tjoe JA, Thompson AM, Wolmark N. Phase II trial assessing accuracy of tumor bed biopsies in predicting pathologic response in patients with clinical/radiological complete response after neoadjuvant chemotherapy in order to explore the feasibility of breast-conserving surgery without surgery: NRG Oncology BR005 [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT1-09-01.