Impact of multifocality and lymph node metastasis on the prognosis and management of microinvasive breast cancer.

BACKGROUND: There are few data on the long-term outcome of patients with microinvasive (T1mi) breast cancer. Moreover, predictors of lymph node involvement and the impact of multifocal microinvasion are not well understood.

METHODS: Patients with T1mi cancer, defined as tumors ≤1 mm, surgically managed at our institute and who underwent axillary lymph node evaluation were identified. Specimen slides were independently reviewed. Multivariate analysis was used to identify factors predictive of lymph node involvement.

RESULTS: Forty-five patients with T1mi cancer were identified. Median patient age was 52 years, and median size of in situ disease was 4 cm. Nine tumors (20.0 %) had more than one focus of microinvasion. Lymph nodes metastasis were identified in 9 patients: 1 macrometastasis (2.2 %), 4 micrometastases (8.9 %), and 4 isolated tumor cells (8.9 %). Seven of 9 patients with lymph node involvement underwent adjuvant chemotherapy. Estrogen receptor-negative invasive disease was a significant predictor of lymph node metastasis by multivariable analysis (p < 0.02). There was also a trend toward lymph node involvement in patients with multifocal microinvasion compared to unifocal disease (33.3 vs. 16.7 %, respectively). At a median follow-up of 83 months, 3 patients (6.3 %) had disease recurrence (1 local, 1 distant, 1 local and distant). All patients with recurrence initially had tumor-free lymph nodes and only one focus of microinvasion.

CONCLUSIONS: Microinvasive breast cancer clearly has the ability to metastasize and recur, but in this series, only 2 % of patients with nodal macrometastasis. Only two patients experienced local recurrence, neither of whom had lymph node metastasis. The importance of identifying nodal micrometastasis in T1mi disease needs to be further explored.