Outcomes for Patients With Micro-Invasive or Small HER2+ Breast Cancer in Northern Sydney Local Health District

Area of Science:

• Oncology
• Breast Cancer Research
• Molecular Diagnostics

Background:

• HER2-positive breast cancer accounts for a significant proportion of diagnoses.
• Microinvasive and small invasive breast cancers require specific treatment considerations.
• Understanding outcomes and care patterns for early-stage HER2+ disease is crucial.

Purpose of the Study:

• To review outcomes for patients with microinvasive and small HER2-positive breast cancers.
• To compare clinicopathological features between different early-stage HER2+ breast cancer subgroups.
• To explore patterns of care, including trastuzumab use, in this patient population.

Main Methods:

• Single-center retrospective study of HER2-positive, pT1mic-bN0M0 breast cancer patients (2006-2022).
• Primary outcome: invasive disease-free survival (iDFS).
• Secondary outcome: overall survival (OS).

Main Results:

• 32 eligible patients were analyzed.
• pT1b disease was associated with higher histological grades and Ki-67 indices.
• 5-year iDFS and OS were 93% for pT1mic/a and 100% for pT1b (p=0.29).
• 66% received adjuvant trastuzumab, associated with larger tumor size and higher grade.
• One recurrence and one death occurred in the pT1a group.

Conclusions:

• Microinvasive and small HER2-positive, node-negative breast cancer generally have favorable outcomes.
• pT1b tumors exhibited higher histological grades and proliferative indices.
• Trastuzumab use was more common in pT1b disease and higher-grade tumors.
• Trastuzumab is recommended for pT1b, but its use in pT1a requires balancing benefits and toxicities.