21-gene recurrence assay in patients receiving intraoperative radiotherapy: are "favorable" characteristics a surrogate for low recurrence?

Oncotype testing in patients undergoing intraoperative radiation for breast cancer

Oncotype DX recurrence score (RS) predicts risk of distant disease recurrence, and can guide chemotherapy recommendations in hormone positive, human epidermal growth factor 2-negative, early stage breast cancer. The present study aimed to evaluate the pattern of oncotype testing, RS and adjuvant treatment in patients undergoing intraoperative radiotherapy (IORT). Single center prospective data registry was queried for patients receiving IORT between October 2011 and February 2017. Patient demographics, tumor characteristics, RS, systemic therapy and recurrence information were analyzed. A total of 150 women with mean age of 70.8 years were included. The majority had invasive ductal cancer (60.6%) with 1.0 cm average tumor size and no lymph node involvement (99%). Oncotype testing was performed in 36 patients (24.3%). Low risk score (<18) was confirmed in 19 women (53%); intermediate risk score (18-30) in 16 women (44%); and high risk score (>30) in one woman (3%). Patients with RS testing had significantly increased tumor sizes (1.2 vs. 1.0 cm; P<0.001) and were younger (68.5 vs. 71.3 years; P=0.02) compared with those not tested. A total of 4/150 patients (2.6%) received chemotherapy; two received chemotherapy based on RS testing. Based on the current selection criteria for IORT, oncotype testing rarely results in a high-risk score or utilization of chemotherapy for IORT patients. The present study supports selective use of RS testing in IORT patients and confirms that biologically low-risk patients are being selected for IORT based on current guidelines.