Evaluation of Biomarkers in Multiple Ipsilateral Synchronous Invasive Breast Carcinomas

Area of Science:

• Oncology
• Pathology
• Biomarker Analysis

Background:

• Current guidelines recommend biomarker testing in additional tumor foci only when morphology or grade differs.
• Multifocal invasive breast carcinomas present challenges for accurate biomarker assessment.

Purpose of the Study:

• To evaluate the clinical significance of testing additional tumor foci for biomarkers in multifocal invasive breast tumors.
• To determine if current guidelines adequately capture clinically relevant discordant biomarker results.

Main Methods:

• Retrospective analysis of 118 patients with ipsilateral synchronous multifocal breast carcinomas.
• Biomarker testing (ER, progesterone receptor, HER2) in additional tumor foci was analyzed.
• Discordance rates and clinical implications were assessed.

Main Results:

• 17% of cases showed discordant biomarker staining between tumor foci.
• Major discordance (negative to positive) occurred in 57% of ER and progesterone receptor discordant cases.
• Testing additional foci would have been recommended in only 33% of discordant cases per guidelines, but 70% of patients with positive smaller foci might have missed adjuvant treatment.

Conclusions:

• Biomarker testing on additional tumor foci is clinically significant, especially when the primary tumor is negative.
• Routine retesting of negative biomarker results in the primary tumor on additional synchronous ipsilateral tumors is proposed.
• Current guidelines may underestimate the importance of testing additional foci in multifocal breast cancer.