Single-dose intraoperative radiotherapy using Intrabeam for early-stage breast cancer

The TARGIT-A trial pre- determined the non-inferiority margin as an absolute difference of 2.5% between Intrabeam® and EBRT in the primary endpoint of local recurrence risk, based on the assumption that the background 5-year local recurrence rate was 6%. [...] In the study published in 2014, authors present results for three overlapping cohorts based on their median length of follow-up: the whole cohort (n=3451) with a median follow up of 2 years and 5 months; the mature cohort consisting of the original 2232 patients with a median follow-up of 3 years and 8 months; and the earliest cohort (n=1222) with a median follow-up of 5 years. [...] Technology Assessment Unit, MUHC Intrabeam® for Early-stage Breast cancer: An Update 6 Local recurrence: The primary outcome was the risk of pathologically confirmed local recurrence (recurrence in the index quadrant of the breast) or loco-regional recurrence (recurrence in the ipsilateral breast or the axilla). [...] The absolute difference in the 5-year risk of local recurrence was 1.0% in the pre-pathology stratum, and 3.7% in the post- pathology stratum, exceeding the non-inferiority margin in the latter case. [...] The authors also report the absolute difference in the binomial proportions of local recurrence (number of recurrences/number of patients) and corresponding 90% CIs for the three different cohorts of women based on their length of follow-up (Table 2).