Background: To elucidate the cause of in-breast recurrence after breast conserving surgery, we analyzed the characteristics of resected specimens histopathologically, especially the surgical margin status. Materials and Methods: 1) Pathological surgical margin positivity was reevaluated in terms of the distance from the resected surgical margin by pathologists from seven institutions in 486 cases with complete stepwise pathological examination. 2) We reviewed pathological specimens including surgical margins from 30 patients with in-breast recurrence for whom serial sections of resected primary breast cancer specimens were available and made comparisons of the time to in-breast recurrence. Results: Cancer cells at the surgical margin were present at a rate of 4.1 % on the surface and 15.2% within 5 mm on the areolar side of the surgical margin. Histopathologically, the reasons for local recurrence after breast conserving therapy included a positive surgical margin (21/30), lymphatic permeation (4/30), and others (5/30). The last category included cases with an inadequate margin diagnosis because of a biopsy scar. Disease-free intervals for the patients without postoperative radiotherapy decreased as the volume of cancer cell nests in the surgical margin increased (P = 0.06). On the other hand, this trend was not observed in the group with postoperative radiotherapy. Conclusion: Adequate materials are essential for accurate evaluation of surgical margin status. Quantitative evaluation of surgical margin status, apart from whether or not radiotherapy was performed, is important for estimating the risk and disease-free period to in-breast recurrence.
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