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

Bridget A. Oppong, Surupa Sen Gupta, Monique Gary, Patricia Wehner, Mihriye Mete, Danjing Zhao, Sulakshana Seevaratnam, Sonali Rudra, Shawna C. Willey


Background: Intraoperative radiotherapy (IORT) has gained momentum for early stage and favorable breast cancers (BC). The 21-gene recurrence assay guides treatment of hormone positive and node-negative BC.
Methods: Analysis of 82 invasive BC treated with breast conservation surgery (BCS) and IORT 2013–2015. Data collection included patient demographics, tumor characteristics, nodal status, recurrence test (RS) and adjuvant therapy.
Results: The mean age was 68. Tumors were stage Ia (86.6%), 3.6% Ib and 9.8% IIa. Of 50 patients (61.0%) with RS testing, 72% (n=36) were low risk (RS 0–17), with 28% (n=14) at intermediate risk (RS 18–30). The 39% (n=32) of patients without RS testing, were more likely to have smaller tumors (1.3 vs. 0.9 cm) and age >70 (P<0.05).
Conclusions: Most patients selected for IORT based on clinical features were indeed low risk based on RS. Given the limited long-term clinical outcome and safety data of this technique, additional investigation is needed.