The 5-Year Paradigm in DCIS of the Breast: Unexpected Lessons From the NSABP B-43 Trial.

Van Bockstal, Mieke [UCL] Libbrecht, Louis [UCL] Galant, Christine [UCL]

TO THE EDITOR: Cobleigh et al1 have reported on the phase III NSABP B-43 trial. This unique randomized cohort provides the first data on the effectiveness of a dual dose of trastuzumab when added to adjuvant whole-breast irradiation after lumpectomy for human epidermal growth factor receptor 2–positive ductal carcinoma in situ (DCIS).1 As the number of ipsilateral breast tumor recurrences (IBTRs) in this extensive cohort was lower than originally estimated, the initially proposed 36% reduction in the IBTR hazard ratio was not achieved.Although not statistically significant, adjuvant rastuzumab was nevertheless associated with a 19% reduction in IBTRs. Subgroup analysis showed that this was because of a marked reduction in in situ IBTRs, without effect on invasive IBTRs.1 Although the authors mentioned two explanations, we would like to highlight another interpretation of this observation. [...]