Clinical significance of microinvasive breast cancer across the different subtypes and human epidermal growth factor receptor 2 expression levels.

PURPOSE

The clinical behavior, prognosis, and management of microinvasive breast cancer (MiBC) is controversial. We aimed to clarify its significance across different subtypes and the role of human epidermal growth factor receptor 2 (HER2) expression in MiBC.

METHODS

We analyzed 1530 patients with T1mi (tumor size ≤ 0.1 cm), node-negative breast cancer who underwent breast conserving surgery or total mastectomy between 2001 and 2020 at the Asan Medical Center (AMC).

RESULTS

When divided into four subtypes, hormone receptor (HR)+/HER2-, HR+ /HER2+ , HR-/HER2+ , and HR-/HER2-, HR-/HER2+ had the highest prevalence rate of 38.5% in MiBC patients. In a median follow-up period of 74 months (0-271 months), 103 (6.7%) patients had recurrent tumor, and 95 (6.2%) had local recurrence. Disease-free survival (DFS) and local recurrence-free survival (LRFS) were worst in the HR-/HER2+ group. The five-year DFS for the HR-/HER2+ group was 92.2%, while it was 97.1% for the HR+/HER2- group (p = 0.024 The five-year LRFS for HER2- patients were better than that of HER2+ MiBC patients, which were 97.1 and 93.8%, respectively (p = 0.010). Univariate and multivariate Cox regression analyses showed that the HR-/HER2+ group had relatively higher risk of recurrence compared to the HR+/HER2- group (hazard ratio [HR] = 2.332, 95% confidence interval [CI] 1.412-3.852, p = 0.001 unadjusted; HR = 3.346, 95% CI 1.408-7.953, p = 0.006 adjusted).

CONCLUSION

HER2 overexpression was significantly associated with adverse clinicopathologic parameters and increased local recurrence risk in MiBC. Therefore, more understanding of the clinical behavior of HER2 in MiBC will enable tailoring of adjuvant therapy for these patients.