Observing more recurrences.

Top Line: What are the long-term outcomes of observation versus adjuvant radiation for good-risk DCIS?

The Study: In RTOG 9804, 636 women with mammogram detected, low or intermediate grade DCIS that was 2.5 cm or less and had 3 mm or more final surgical margins were randomized to observation or whole breast radiation after lumpectomy. Adjuvant tamoxifen was optional, however ⅔ of patients received it. We’ve previously known that, at 7 years, radiation significantly reduced ipsilateral breast recurrence (IBR) events from 7.2→ 0.8%. But we also know that breast cancer is a long game with a considerable rate of recurrence beyond 10 years. The long-term outcomes of 9804 continue to show that adjuvant RT significantly reduces the rate of IBR from 9.2 → 1.5% at 10 years and from 15.1 → 7.1% at 15 years. Put another way, radiation increased the median time to IBR from 7 → 11.5 years. In the observation arm, 76% of IBR were in the original quadrant compared to 56% in the radiation arm. Most IBR were invasive (63%), and again radiation reduced invasive IBR from 4.3 → 0.4% at 10 years and from 9.5 → 5.4% at 15 years. There was no difference in the rate of contralateral breast events between arms. The rate of late grade 3 toxicity was a whopping 1% with radiation. So, it’s important to consider what exactly we’re omitting and why when it comes to adjuvant radiation for DCIS in women who will live 15+ years after diagnosis.

TBL: Adjuvant radiation halves the rate of ipsilateral breast recurrences at 10 and 15 years with minimal late toxicity in women with good-risk DCIS. | McCormick, J Clin Oncol 2021