Confidence boost.

Top Line: What is the role of tumor bed boost and hypofractionation for DCIS?

The Study: While this might sound like a trick question, the use of hypofractionation and tumor bed boost for DCIS has largely been extrapolated from randomized trials of patients with mostly invasive breast cancer. BIG 3-07/TROG 07.01 was a huge randomized trial that evaluated the role of fractionation and tumor bed boost for DCIS. Eligible patients had non-low risk DCIS, which included any of the following risk factors: age <50, symptomatic presentation, palpable tumor, tumor size ≥1.5cm, multifocal disease, intermediate or high grade, central necrosis, comedo histology, or a radial margin <1cm (but ≥1mm). There were two key comparisons: boost versus no boost and conventional fractionation vs moderate hypofractionation. 1608 patients across >150 centers in 11 countries were enrolled. While all centers enrolled patients in the boost vs no boost randomization, centers were allowed to choose whether A) to randomize to CF or HF (31%), B) treat everyone with CF (36%), or C) treat everyone with HF (33%). CF consisted of 50Gy in 25 fractions and HF consisted of 42.56Gy in 16 fractions. The boost dose was 16Gy in 8 fractions regardless of fractionation.  It is important to note that only 13% of patients received endocrine therapy. At 5 years, the addition of a boost significantly improved freedom from local recurrence (97.1% v 92.7%). Most recurrences were in the original quadrant (73% boost, 81% no boost) and were in situ disease (55% boost, 56% no boost). There was no difference in freedom from recurrence with CF v HF in the randomized arm (94.4% v 93.7%) or among the entire population (94.9% v 94.9%). Boost and tumor size were the only factors significantly associated with local recurrence in multivariate analysis. The rate of acute grade 2+ dermatitis was also higher with boost (45% v 29%. The rate of late grade 2+ breast pain (14% v 10%) and induration (14% v 6%) were higher with boost. There were no significant differences in cosmetic outcomes with respect to fractionation.

TBL: Tumor bed boost improves local control 4.4% at 5 years among patients with non-low risk DCIS while modestly increasing acute and late toxicity. There is no difference in recurrence or cosmetic outcomes when using moderate hypofractionation versus conventional fractionation. | Chua, Lancet 2022