Clinical Utility of Oncotype DX Testing in Synchronous Bilateral and Unilateral Multifocal Breast Cancer

Area of Science:

• Oncology
• Genomics
• Breast Cancer Research

Background:

• Multifocal breast cancer (MFBC) presents challenges in treatment selection.
• Genomic profiling, like Oncotype DX, aids in adjuvant chemotherapy decisions.
• Discordance in genomic profiles between synchronous tumors can impact treatment efficacy.

Purpose of the Study:

• To determine the frequency and clinical correlates of Oncotype DX Recurrence Score (RS) differences in synchronous tumors of MFBC.
• To evaluate the therapeutic implications of RS discordance on adjuvant chemotherapy recommendations.
• To compare RS variability between bilateral and unilateral MFBC.

Main Methods:

• Retrospective analysis of 131 patients with hormone receptor-positive, HER2-negative early-stage breast cancer.
• Oncotype DX testing performed on at least two synchronous tumor foci.
• Multivariable regression to identify factors associated with RS differences.
• Kaplan-Meier analysis for disease-free survival.

Main Results:

• RS risk-category discordance observed in 21% (bilateral) and 24.7% (unilateral) MFBC.
• Discordance led to chemotherapy escalation in 50% of cases.
• Progesterone receptor score difference linked to RS difference in bilateral disease.
• HER2, progesterone, and estrogen receptor score differences associated with RS difference in unilateral disease.
• Higher RS correlation between paired tumors in unilateral vs. bilateral MFBC.

Conclusions:

• Genomic heterogeneity is frequent in synchronous MFBC, impacting chemotherapy recommendations.
• Single-lesion testing may underestimate tumor variability.
• Multilesion testing is recommended for selected MFBC patients to optimize treatment selection.