Clinicopathologic analysis of a large series of microinvasive breast cancers.

Clinical management of microinvasive breast cancer (Tmic) remains controversial. Although metastases are infrequent in Tmic carcinoma patients, surgical treatment typically includes lymph node sampling. The objective of this study was to determine the rate and predictors of lymph node metastases, recurrence, and survival in a large series of Tmic breast carcinomas. Consecutive cases of Tmic were identified within our health care system from 2001 to 2015. We reviewed results of lymph node sampling and other pathologic factors including hormone receptor/HER2 status, associated in situ tumor size/grade, margin status, number of invasive foci, surgical/adjuvant therapies, and recurrence/survival outcomes. In this cohort, 294 Tmic cases were identified with mean follow-up of 4.6 years. Of 260 patients who underwent axillary staging, lymph node metastases were identified in 1.5% (all of which were ductal type). All Tmic cases with positive lymph node metastases had associated DCIS with size > 5 cm (5.3-8.5 cm) compared to a median DCIS tumor size of 2.5 cm (0.2-19.0 cm) for the entire cohort. No lymph node metastases were seen with microinvasive lobular carcinoma. During the follow-up period, there were no regional/distant recurrences or breast cancer-associated deaths in a mean follow-up period of 4.6 years. Two patients developed subsequent ipsilateral breast cancer (DCIS) in a different quadrant than the original Tmic. Clinical behavior of microinvasive breast cancer in this series is similar to DCIS. Lymph node metastases are uncommon and were only seen with ductal type microinvasive carcinoma. Our data suggest limited benefit for routine node sampling and support management of Tmic similar to DCIS, particularly for patients with DCIS < 5 cm in size.