Understanding the molecular basis of histologic grade

Area of Science:

• Oncology
• Genomics
• Molecular Biology

Background:

• Histologic grading of breast cancer evaluates tubule formation, nuclear pleomorphism, and mitotic count to assess proliferation and differentiation.
• Traditional grading suggests distinct molecular origins for low (grade 1) and high (grade 3) grade tumors.
• Current proliferation markers like Ki-67 are not always routinely used in clinical practice.

Purpose of the Study:

• To investigate the role of genome-wide gene expression in breast cancer grading.
• To develop and validate a gene expression grade index (GGI) for breast cancer.
• To re-evaluate the clinical relevance of intermediate histologic grade 2 breast tumors.

Main Methods:

• Utilized microarray technology for genome-wide gene expression profiling in breast cancer.
• Developed a gene expression grade index (GGI) based on comprehensive gene expression data.
• Conducted a large meta-analysis of publicly available gene expression and clinical data.

Main Results:

• The GGI challenges the clinical relevance of intermediate histologic grade 2, reclassifying patients into high and low recurrence risk groups.
• GGI identified clinically relevant subgroups within estrogen receptor-positive breast carcinomas.
• A meta-analysis revealed 4 stable molecular subgroups of breast cancer (ER-/HER-, HER2+, ER+/HER2-), with ER+/HER2- further divided by proliferation.
• Proliferation emerged as the central driving factor for the efficacy of various breast cancer prognostic signatures.

Conclusions:

• Gene expression profiling offers a powerful tool to refine breast cancer grading beyond traditional morphologic features.
• The GGI provides a more precise prognostic stratification, particularly for intermediate grade tumors.
• Proliferation is a fundamental determinant of breast cancer behavior and a unifying factor across molecular subgroups.