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Top Line: Is there any long-term data comparing 5-fraction whole breast radiation to conventional fractionation?

The Study: The FAST trial (no, not the FAST-Forward trial) was initially reported in 2011, and presented at ASTRO 2018. It compared 50 Gy in 25 fractions to 28.5 Gy and 30 Gy in 5 weekly fractions. Who was eligible? Low-risk women over 50 with <3 cm invasive tumors following R0 lumpectomy who didn’t need a boost and didn’t get chemotherapy. Here, we have the 10-year results for control and physician-assessed late effects, as well as 5 year results of photographic breast appearance. At 5 years, 80% of patients had no change in photographic appearance, 18% had mild change, and 3% had marked change. If we look at the 50/25 fractions reference and 28.5/5 fractions arm at 5 years, respectively, there are similar rates of mild (16% versus 17%) and marked (2% versus 2.4%) changes in appearance. But compared to the 50/25 arm, rates were worse for the 30/5 arm: mild (21%) and marked (4%) changes. Physician-assessed normal tissue effects (NTE)—mainly breast shrinkage—at 10 years were again fairly similar for 50/25 (8% moderate, 0.8% marked) and 28.5/5 (13% moderate, 1.5% marked). But, again, 30/5 was worse (14% moderate, 5% marked). The absolute difference in any moderate/marked NTE at 10 years when compared to 50/25 was +5% for 28.5/5 and +9% for 30/5. The cumulative incidence of ipsilateral breast tumor events at 10 years was really low (1.3%) and there were no obvious differences between groups.

TBL: At 10 years, there is no significant difference in the rate of local control or moderate/marked late toxicity for women with low-risk breast cancer receiving 28.5 Gy in 5 weekly fractions. | Brunt, J Clin Oncol 2020