• Danielle N Margalit, Meera Sreedhara, Yu-Hui Chen, Paul J Catalano, Paul L Nguyen, Mehra Golshan, Beth A Overmoyer, Jay R Harris, and Jane E Brock.
• Department of Radiation Oncology, Brigham & Women's Hospital/Dana-Farber Cancer Institute, Boston, MA, USA.
• Ann. Surg. Oncol. 2013 Mar 1; 20 (3): 811-8.

BackgroundContemporary clinical outcomes of microinvasive breast cancer (MIBC), defined as no focus >1 mm, are not well characterized. We document the immunophenotype, incidence of axillary metastases, and rate of recurrence in a well-defined case series.MethodsWe reviewed 83 consecutive patients with MIBC from 1997 to 2005. Estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER-2/neu) receptor status were assessed. The cumulative incidence of local recurrence (LR) and nodal/distant recurrence was calculated. Predictors of recurrence were identified and effect estimates determined.ResultsFifty-two patients (63%) underwent breast-conserving therapy (BCT) and 31 (37%) underwent mastectomy. Sixty-one percent had ER-positive disease and 49% had HER-2/neu-positive disease. Three (4%) of 68 patients with sentinel node mapping or axillary dissection had single node micrometastases, and none had macrometastases or multiple nodes involved. Median follow-up was 6.4 years, with 6 LRs, 2 regional nodal recurrences, and 2 concurrent local/distant recurrences. The 5-year cumulative incidence of recurrence (local, nodal, or distant) was 5.3% (95% confidence interval [CI] 2.0-13.4) for all patients, and among BCT patients, the 5-year cumulative incidence of LR was 4.2% (95% CI 0.7-12.7). HER-2/neu overexpression was not associated with recurrence (P = 0.46). Close/positive margins (≤2 mm) were significantly associated with an increased risk of LR after BCT or mastectomy (hazard ratio 8.8; 95% CI 1.6-48.8; P = 0.003).ConclusionsMIBC has a favorable prognosis, and HER-2/neu overexpression, although highly prevalent, is not significantly associated with recurrence. Axillary metastases at diagnosis are small and infrequent. The cumulative incidence of LR after BCT is acceptable; however, our data confirm that negative margins (>2 mm) are required for optimal BCT outcomes.

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