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

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Abstract
The extent of positivity of the final excision margin in relationship to other relevant factors was evaluated as a predictor for local recurrence after breast conservation therapy (BCT). As part of an institutional practice policy for BCT in 509 stage I/II breast carcinomas, 105 cases had a final excision margin, which was positive. The median age for this cohort was 58 years and the median follow‐up was 86 months. All positive margin patients received 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 excision margin was graded according to a four‐point scale: focal, minimal, moderate, extensive. Cases were then analyzed for local failure according to EOP grade, histology, age, tumor size, total excision volume, re‐excision, tamoxifen therapy, and chemotherapy. A focal or minimal EOP grade was found in 70% of specimens while an additional 26% were moderate or extensive. The incidence of invasive carcinoma with prominently associated DCIS was significantly greater in cases with an EOP grade of moderate/extensive. There were nine ipsilateral breast recurrences, eight of which could be evaluated 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 model found that the only variable significantly related at the P ≤ 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. Radiat. Oncol. Invest. 7:111–117, 1999.

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