PRIME headlines.

Top Line: Who is ready to rehash the benefits of radiation following breast-conservation for low risk breast cancer?

The Study: PRIME II was a randomized phase 3 trial in which 1326 women 65 and older with low risk breast cancer were randomized to radiation or no radiation after breast conservation surgery. Low risk criteria included hormone receptor positive, node negative, ≤3 cm tumor, and negative margins. Grade 3 histology or LVI (but not both) were allowed, but this was a small minority (<5%) of cases. Everyone received the obligatory 5 years +of adjuvant endocrine therapy. In the radiation arm, everyone received 40-50 Gy in 15-20 fractions whole breast RT +/- a boost. Before we get too far into things, let us recall the trial design. PRIME II was designed to show that there was no difference in the primary outcome of local recurrence with or without adjuvant radiation. Here we have the 10-year outcomes where the cumulative incidence of local breast cancer recurrence was 10-fold lower with adjuvant radiation (0.9% v 9.5%). As expected, there were no differences in distant recurrence (3% v 1.6%) or overall survival (80.7% v 80.8%).

TBL: In women 65 or older with low-grade, hormone receptor positive breast cancer that is ≤3 cm, the risk of breast cancer recurrence at 10 years is roughly 1% with adjuvant radiation and 10% without with no difference in survival. | Kunkler, N Engl J Med 2023