Targeted intraoperative radiotherapy tumor bed boost during breast conserving surgery after neoadjuvant chemotherapy in hormone receptor positive HER2 negative breast cancer.

Abstract

e12090 Background: Targeted intraoperative radiotherapy (TARGIT – IORT) as a tumor bed boost during breast conserving surgery is an established option for women with early breast cancer. In a previous study our group could show a beneficial effect of TARGIT-IORT on overall survival after neoadjuvant chemotherapy compared to an external boost in an unselected cohort. In this study we present an analysis of the hormone receptor positive HER2 negative subgroup. Methods: In this non-randomized cohort study involving 46 hormone receptor positive HER2 negative patients after NACT we compared outcomes of 21 patients who received a tumour bed boost with IORT (TARGIT-IORT) during lumpectomy versus 25 patients treated in the previous 13 months with external (EBRT) boost. All patients received whole breast radiotherapy. Disease free survival (DFS) and overall survival (OS) were compared. Results: There were no statistical differences between the two groups regarding tumor size, grading, nodal status and pCR rates. Median follow up was 49 months. Whereas DFS was not significantly different between the groups the 5-year Kaplan-Meier estimate of OS was significantly better by 21% with IORT: TARGIT-IORT 0 events 100%, EBRT 5 events 79%, log rank p = 0.028. Conclusions: Although our results have to be interpreted with caution due to a possible selection bias and the small numbers, we could show that the improved OS as previously demonstrated in our dataset for TARGIT-IORT during lumpectomy after neoadjuvant chemotherapy as a tumor bed boost compared to an external beam radiotherapy boost is driven by the hormone receptor positive HER2 negative subgroup. These data give further support to the inclusion of such patients in the TARGIT-B (Boost) randomised trial that is testing whether IORT boost is superior to EBRT boost and to the analysis of subgroups based on tumor biology in this trial.