Boost HER or not?

Top Line: Can tumor bed boost be omitted in some women with HER2+ breast cancer? 

The Study: The ASTRO Breast Cancer Guidelines suggest omitting boost in older women with hormone receptor-positive breast cancer. Multiple RCTs have demonstrated a reduction in breast tumor recurrence with the addition of a radiation boost to the lumpectomy cavity in the setting of breast conservation therapy (EORTC 22881 & Lyon). This secondary analysis of the landmark HERA trial takes a look at the risk of recurrence in women with HER2+ breast cancer who received trastuzumab and whole breast radiation with or without a boost. Over 1000 patients (21% of the entire HERA cohort) were eligible for the analysis. Importantly, tumor bed boost was not a study question and thus was not standardized in the trial. Given that inherent bias, there were no major differences in baseline patients characteristics (except more right-sided tumors in the boost group). Overall, ~40% received a boost and 60% did not. At a median follow up of 11 years, there was no significant difference in the rate of local recurrence with (6.35%) or without (7.8%) a boost. Even looking at age and hormone receptor status didn’t reveal any glaring differences in local control. In the EORTC trial, the absolute reduction in IBTR was around 4-5%, so this data at least suggests that a tumor bed boost may not be associated with a large improvement in local control in women with HER2+ breast cancer. 

TBL: Among women with HER2+ breast cancer receiving whole breast radiation on the HERA trial, tumor bed boost wasn’t associated with a reduced rate of local recurrence. | Jaoude, Int J Radiat Oncol Biol Phys 2020