Microinvasive Breast Cancer: ER, PR, and HER-2/neu Status and Clinical Outcomes after Breast-Conserving Therapy or Mastectomy

Contemporary 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.

We 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.

Fifty-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).

MIBC 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.