Is the risk of local recurrence higher for microinvasive breast cancer vs. early stage invasive breast cancer?

Purpose: The prognosis and optimal treatment for microinvasive breast cancer is controversial with some data indicating a higher local recurrence with microinvasive disease as compared to early-stage invasive breast cancer. The goal of our study was to compare long-term outcomes between patients with T1mi disease and early-stage breast cancer after breast-conserving surgery and whole breast irradiation (WBI).

Methods: We reviewed all patients treated at our institution from 2013 to 2019 with T1mi-T2N0 disease. Cox proportional hazard model was used to find independent prognostic variables associated with local recurrence (LR). Survival curves were analyzed by Kaplan-Meier.

Results: We found 1155 patients with 56 (4.8%) having T1mi disease. The 5-year local recurrence rate was 5.3% in patients with T1mi disease and 1.2% in patients T1-2 disease (HR = 2.73; 95% CI 0.43, 17.9; p = 0.09). On Cox multivariate analysis, younger age, positive margins and the need for re-excision were prognostic for LR. Out of the 3 patients with microinvasive disease who developed a local recurrence, two had DCIS < 2 mm from the margin and the third patient underwent two re-excisions due to DCIS margins < 2 mm.

Conclusions: Our study showed that patients with microinvasive disease treated with hypofractionated WBI had a numerically higher 5-year local recurrence rate than patients with T1a-2 disease though this difference was not statistically significant. Given the rarity of microinvasive disease, further work is needed to define optimal surgical and adjuvant management and to better clarify the risk of local recurrence in this patient population.