Effect of margin width on local recurrence in triple-negative breast cancer patients treated with breast-conserving therapy

Background. The effect of increasing negative margin width after breast-conserving therapy (BCT) on local recurrence (LR) is controversial. LR rates vary by subtype, with the highest rates seen in triple-negative breast cancer (TNBC). This study examined LR rates in relationship to margin width in TNBC treated with BCT. Methods. Women with TNBC who underwent BCT between 1999 and 2009 were identified. Margins were defined as positive (ink on tumor), 0.1-2.0, and 2 mm. Patients with positive margins were excluded. Statistical comparisons were by t test, Fisher's exact test, and Wilcoxon rank sum test. Cumulative incidence of LR was compared by competing-risks methodology. Results. Of 535 cancers, 71 had margins ≤2 mm and 464 had margins >2 mm. At a median follow-up of 84 months (range 8-165 months), there were 37 local, 18 regional, and 77 distant recurrences or deaths as first events. Ten patients had a locoregional recurrence before planned radiotherapy and were excluded from cumulative incidence analyses. The cumulative incidence of LR at 60 months for margins ≤2 mm was 4.7 % (95 % confidence interval 0-10.0) and for >2 mm was 3.7 % (1.8, 5.5) (p = 0.11). After controlling for chemotherapy and tumor size, there was no difference in LR between the two margin groups (p = 0.06). A difference in the risk of distant recurrence or death was not observed (p = 0.53). Conclusions. Margin width of >2 mm was not associated with reduced LR rates. These data support a negative margin definition of no ink on tumor, even in this high-risk TNBC cohort.