Objectives/purpose: To review the outcomes for patients with microinvasive and small HER2+ breast cancers, compare the clinico-pathological features, and explore the patterns of care in North Sydney Local Health District (NSLHD).
Sample and setting: This single-center retrospective study aimed to recruit 50 patients with HER2+, pT1mic-bN0M0 disease in NSLHD between 2006 and 2022. Thirty-two patients were included after applying exclusion criteria.
Procedures: Eligible patients were identified from the pathology database at Royal North Shore Hospital, and their clinic-pathological data and treatment details were collected. Invasive disease-free survival (iDFS) and overall survival (OS) were estimated by Kaplan–Meier analysis. Univariate linear regression was used to identify pathological factors associated with trastuzumab prescription. Due to the small sample size and low number of events, confidence intervals for iDFS and OS were not included.
Results: Median follow-up time for the cohort was 62 months (IQR 37-89 months) with a median age at diagnosis of 60 years. Patients with pT1b disease had higher histological grades (p = 0.013) and Ki-67 index (p = 0.030), with a higher rate of trastuzumab administration (p = 0.004). One recurrence and one death occurred in the pT1a group. The 5-year iDFS and OS were 93% for the pT1mic/a group and 100% for the pT1b group (p = 0.29). Sixty-six percent of patients received adjuvant trastuzumab. Trastuzumab prescription was associated with larger tumor sizes (p = 0.008) and higher histologic grades (p = 0.023).
Conclusion and clinical implications: Patients with microinvasive or small HER2+ node-negative breast cancer experience favorable outcomes. The pT1b group had higher histological grades and proliferative indices. Patients with pT1b disease or higher tumor grades were more likely to receive trastuzumab. While trastuzumab is recommended for pT1b disease with strong evidence, its use in pT1a disease should be balanced against its unclear benefits and known toxicities.