Extent of margin positivity as a predictor for local recurrence after breast conserving irradiation

The extent of positivity of the final excision margin in relationship to ot her relevant factors was evaluated as a predictor for local recurrence afte r breast conservation therapy (BCT). As part of an institutional practice p olicy for BCT in 509 stage I/II breast carcinomas, 105 cases had a final ex cision margin, which was positive. The median age for this cohort was 58 ye ars and the median follow-up was 86 months. All positive margin patients re ceived whole breast irradiation to 50 Gy-50.4 Gy followed by a boost to the tumor bed for an additional 20 Gy. The extent of positivity (EOP) of the e xcision margin was graded according to a four-point scale: focal, minimal, moderate, extensive. Cases were then analyzed for local failure according t o EOP grade, histology, age, tumor size, total excision volume, re-excision , tamoxifen therapy, and chemotherapy. A focal or minimal EOP grade was fou nd in 70% of specimens while an additional 26% were moderate or extensive. The incidence of invasive carcinoma with prominently associated DCIS was si gnificantly greater in cases with an EOP grade of moderate/extensive. There were nine ipsilateral breast recurrences, eight of which could be evaluate d for EOP grade. All recurrences were in or near the previous biopsy cavity . A Kaplan-Meier plot of freedom from local failure showed a significant (P = 0.008) difference between cases grouped by EOP grade of focal/minimal as compared to moderate/extensive. A Cox proportional hazards regression mode l found that the only variable significantly related at the P less than or equal to 0.05 Level to local failure was an EOP grade of moderate/extensive . For breast excision specimens with a positive final margin, an EOP grade of moderate/extensive is a predictor for local recurrence after BCT, which may be independent of other variables such as age or histology. (C) 1999 Wi ley-Liss, Inc.