Identification of molecular apocrine breast tumours by microarray analysis

Area of Science:

• Oncology
• Genomics
• Molecular Biology

Background:

• Previous breast cancer studies identified luminal and basal tumor classes based on estrogen receptor alpha (ER) gene expression.
• Tumor classification is crucial for understanding breast cancer heterogeneity and guiding treatment strategies.

Purpose of the Study:

• To identify novel breast cancer subtypes using gene expression profiling.
• To characterize a newly identified 'molecular apocrine' breast tumor group based on steroid receptor activity.

Main Methods:

• Gene expression microarrays (Affymetrix U133A) were used to analyze 49 breast tumor samples.
• Principal components analysis and hierarchical clustering were employed for tumor classification.
• Statistical tests (Kolmogorov-Smirnov, Wilcoxon) were used to assess gene expression patterns and significance.

Main Results:

• A distinct 'molecular apocrine' breast tumor group was identified, characterized by increased androgen signaling.
• This group is androgen receptor (AR) positive and ER-negative, with histological apocrine features.
• Estrogen signaling is highest in luminal tumors, while androgen signaling is highest in molecular apocrine tumors. ERBB2 amplification is more frequent in the molecular apocrine group.

Conclusions:

• Breast tumors can be classified into three groups based on steroid receptor activity: luminal (ER+ AR+), basal (ER- AR-), and molecular apocrine (ER- AR+).
• Molecular apocrine tumors represent a significant subset (8-14%) of breast cancers in published studies.
• This classification provides a more refined understanding of breast cancer subtypes and their molecular drivers.