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Breast cancer treatment is a complex and evolving field, particularly for hormone receptor-positive (HR+), HER2-negative early-stage breast cancer (EBC). Genomic tools like the MammaPrint index are instrumental in tailoring treatment strategies. The study by Joyce O’Shaughnessy and colleagues presented at the ASCO Annual Meeting sheds light on how MammaPrint can influence chemotherapy decisions and outcomes, emphasizing the importance of personalized medicine in improving patient care.

Breast cancer is not a uniform disease; it varies significantly among individuals. HR+HER2- breast cancer, while generally having a better prognosis, still poses a substantial risk of recurrence. Traditional treatment approaches include surgery, radiation, and adjuvant therapies such as chemotherapy and hormone therapy. The challenge lies in identifying which patients will benefit most from chemotherapy, particularly when considering the potential side effects.

The MammaPrint test evaluates the expression of 70 genes to classify tumors into Low-Risk or High-Risk for distant recurrence. This genomic signature helps clinicians decide whether a patient can safely forgo chemotherapy or if they need this aggressive treatment to reduce the risk of recurrence. This study explores MammaPrint’s utility in guiding chemotherapy choices, specifically comparing taxane and cyclophosphamide (TC) with anthracycline + TC (AC-T).

This study assessed the association between the MammaPrint index and three-year Recurrence-Free Interval (RFI) in HR+HER2- EBC patients treated with TC or AC-T chemotherapy. Conducted as part of the FLEX Study (NCT03053193), it included stage I-III breast cancer patients who underwent MammaPrint testing and consented to detailed transcriptome and clinical data collection.

The study analyzed data from 614 patients with HR+HER2- MammaPrint High Risk and BluePrint (BP) Luminal B-Type tumors. These high-risk tumors were further divided into High 1 (H1) or High 2 (H2) based on the MammaPrint index. The primary focus was on the three-year RFI, defined as the time from diagnosis to local-regional recurrence, distant recurrence, or breast cancer-specific death. Differences in RFI between H1 and H2 tumors, stratified by chemotherapy regimen, were evaluated using Kaplan-Meier analysis and log-rank tests.

The study’s findings underscore the differential impact of chemotherapy regimens based on the MammaPrint index classification:

  • Recurrence-Free Interval (RFI): Patients with H2 Luminal B-Type tumors treated with TC had a significantly worse three-year RFI (86.4%) compared to those with H1 Luminal B-Type tumors (97.1%). This suggests that H2 tumors are less responsive to TC alone. Conversely, there were no significant differences in RFI for patients treated with AC-T, indicating that anthracycline may mitigate the risk of recurrence for H2 tumors.
  • Chemotherapy Regimen Optimization: The results highlight the need to tailor chemotherapy regimens based on genomic profiling. Patients with H2 Luminal B-Type tumors appear to benefit more from anthracycline-based chemotherapy, whereas H1 tumors may not require such aggressive treatment.

This study is important for several reasons:

  1. Enhanced Treatment Precision: By utilizing the MammaPrint index, clinicians can better personalize chemotherapy regimens, ensuring patients receive the most effective treatment while avoiding unnecessary side effects.
  2. Improved Patient Outcomes: The study provides clear evidence that genomic profiling can identify patients who benefit most from specific chemotherapy regimens, potentially improving long-term outcomes and quality of life.
  3. Guiding Future Research: These findings lay the groundwork for further research into the biological mechanisms underlying differential chemotherapy responses and the integration of additional biomarkers to refine treatment strategies.

The insights here underscore the transformative potential of genomic profiling in breast cancer treatment. The study demonstrates that the MammaPrint index can significantly influence chemotherapy decisions, tailoring treatment to individual tumor biology and enhancing patient outcomes. Integrating genomic signatures into clinical practice will be crucial for delivering optimal, patient-specific care as personalized medicine advances.

By leveraging the latest research and incorporating genomic profiling into treatment planning, healthcare professionals can more effectively navigate the complexities of breast cancer treatment, offering patients new hope for improved survival and quality of life. This study represents a significant step in personalizing cancer treatment and ensuring that each patient receives the most appropriate care for their unique disease profile.


  1. O’Shaughnessy J, et al. J Clin Oncol 42, 2024 (suppl 16; abstr 511)
  2. MammaPrint, BluePrint, and Full-genome Data Linked With Clinical Data to Evaluate New Gene EXpression Profiles (FLEX)
Zachary Moore

Author Zachary Moore

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