MammaPrint Assay Identifies Subgroup Benefiting from Extended Letrozole Therapy in Early-Stage Breast Cancer

MammaPrint Assay's Role in Extended Letrozole Therapy

A groundbreaking analysis from the NSABP B-42 trial has shed new light on the use of the MammaPrint (MP) genetic assay in predicting the benefits of extended letrozole therapy (ELT) for patients with hormone receptor-positive early-stage breast cancer. The study, led by Priya Rastogi, MD, of the University of Pittsburgh Medical Center Hillman Cancer Center, challenges previous assumptions by identifying a subgroup of patients who stand to gain the most from ELT.

Key Findings

• No Significant Difference in Primary Endpoint: The study found no significant difference in the 10-year distant recurrence rate between letrozole and placebo groups among patients categorized as MP high-risk or low-risk.
• Exploratory Analysis Reveals Benefits: An exploratory analysis highlighted a significant benefit in 10-year distant recurrence for 908 patients classified as "low but not ultra-low" risk.
• Secondary Endpoints Show Promise: Contrary to the primary hypothesis, significant benefits for disease-free survival and breast cancer-free interval were observed in low-risk patients, not high-risk ones.

Implications for Clinical Practice

Dr. Rastogi emphasized the importance of these findings, stating, "These data could have important clinical implications in patient selection beyond clinical risk assessment for extended endocrine therapy." However, she also cautioned that MP assay scores should not currently be used to decide on the duration of endocrine treatment, as further validation in independent trials is necessary.

Understanding the Findings

The study suggests that patients with MP-high risk tumors may not benefit from extended endocrine therapy due to intrinsic decreased sensitivity to hormone therapy. This insight, coupled with the potential benefits observed in low-risk patients, underscores the need for personalized treatment approaches based on genomic classification.

Conclusion

This study represents a significant step forward in understanding the role of genomic assays in tailoring breast cancer treatment. By identifying which patients are most likely to benefit from extended endocrine therapy, oncologists can better personalize treatment plans, potentially improving outcomes for those with hormone receptor-positive early-stage breast cancer.

The study was supported by Agendia, NIH, the Korea Health Technology R&D Project, and Novartis, which provided letrozole and placebo. Dr. Rastogi reported financial relationships with Genentech/Roche, Lilly, and AstraZeneca.