HER2 Low Expression in Primary Male Breast Cancer

Area of Science:

• Oncology
• Pathology
• Genetics

Background:

• HER2-targeting antibody drug conjugates (ADCs) offer new treatment options for HER2 low female breast cancer (FBC).
• The prevalence and impact of HER2 low expression in male breast cancer (MBC) remain understudied.
• HER2 low expression does not appear to define a distinct subtype in FBC.

Purpose of the Study:

• To evaluate the prevalence of HER2 low expression in primary male breast cancer (MBC).
• To correlate HER2 low expression with patient characteristics and tumor biology in MBC.
• To explore the potential for MBC patients to benefit from HER2-targeting therapies.

Main Methods:

• Histological specimens from 120 primary invasive MBC patients (1995-2022) were analyzed.
• HER2 immunostaining and in situ hybridization were performed and evaluated using ASCO/CAP guidelines.
• Correlation analysis was conducted between HER2 low expression, tumor characteristics, and patient outcomes.

Main Results:

• 32.5% of MBC cases were classified as HER2 low.
• No statistical correlation was found between HER2 low expression and tumor biological characteristics or patient survival.
• HER2 positivity (3+) was observed in 3.3% of cases, with other categories including HER2 2+, HER2 1+, and HER2 zero.

Conclusions:

• HER2 low expression occurs in primary MBC, but does not constitute a new subtype.
• A significant proportion of MBC patients may be candidates for HER2-targeting ADCs.
• Further research is needed to fully understand HER2 low breast cancer in both sexes.