Title: Improved Neoadjuvant Chemosensitivity Prediction for HR+HER2- Breast Cancer Patients with MammaPrint High 2 risk in the FLEX Trial and Descriptive Analysis of Dutch Routine-Testing

Publication: 21st Bossche Mamma Congress 2024, Abstract P07

Authors:Joyce O’Shaughnessy,  Thijs van Dalen, Peter Nieboer, Jelle Klinkhamer, Darina Pronin, Andrea Menicucci, William Audeh, FLEX Investigators’ Group

Background: Hormone receptor-positive (HR+), HER2-negative early-stage breast cancer (EBC) displays notable heterogeneity and diverse responses to neoadjuvant chemotherapy (NCT). Utilizing genomic profiling has become crucial in guiding pre-operative treatment decisions by predicting the probability of achieving a pathological complete response (pCR) and demonstrating chemosensitivity. The MammaPrint (MP) test, analyzing 70 genes, effectively categorizes patients with EBC into Low or High-Risk groups for distant metastasis development 1-3. Further refinement of the High-Risk group into High 1 (H1) and High 2 (H2)subcategories has demonstrated significantly improvedpCRrates in MP H2 tumorscompared to MP H1, particularlywith NCT or targeted therapies such as immunotherapy. This study evaluates the efficacy of MP H1/H2 risk stratification as a biomarker for chemosensitivity in patients with HR+HER2- EBC participating in the real-world FLEX Trial 4,5. Furthermore, data from the observational FLEX Trial and routine-testing in the Netherlands from 2019-2023 submitted to Agendia are compared.

Methods: This analysis includes patients with HR+HER2-, MP High Risk tumors with available treatment response data from the FLEX Trial (NCT03053193) and data from routine diagnostics. This analysis specifically focuses on patients with HR+, HER2-negative, MP High Risk tumors for which treatment response data are available. Within the MP High Risk category, patients were further stratified into two groups: H1 (MP index 0.000 to -0.569) and H2 (MP index -0.570 to -1.000). Additionally, BluePrint classified tumors into Luminal-, HER2-, or Basal-Type categories. In the FLEX cohort, the endpoint of pathological complete response (pCR) was evaluated in a subset of patients who received neoadjuvant chemotherapy (NCT), totaling n=260.


  • MammaPrint H1 and H2 in FLEX
    • MammaPrint classified 64% of tumors as H1 and 36% as H2.
    • There was no significant difference in menopausal status, tumor stage, or lymph node status between the two groups.
    • While a majority (80%) of H2 tumors were classified as Grade 3, only 60% of tumors classified as Grade 3 were identified as H2.
    • The majority (97%) of H1 tumors were classified as Luminal B, in contrast to H2 tumors, where 46% were classified as Luminal B and 54% were classified as Basal according to BP classification.
    • While H2 tumors were more prevalent in Low and Medium ER-staining groups, 23% of High ER-staining tumors were identified as H2.
  • Difference in pCR rate between MP H1 and H2 tumors
    • pCR rate was significantly higher in H2 tumors compared to H1 tumors.
    • H1 tumors had a pCR rate of 6.6%, whereas H2 tumors had a pCR rate of 28.7%.
  • Difference in pCR rates by BP subtypes
    • Basal-Type H2 tumors, with a sample size of 49, showed the highest pCR rate of 38.8%.
    • Within the group of BP Luminal B tumors, those categorized as MP H2 had a notably higher pCR rate compared to those categorized as MP H1.
    • Luminal B H1 tumors had a pCR rate of 6.3%, while Basal H1 tumors showed a pCR rate of 16.7%.


The real-world data from the FLEX registry of MammaPrint and BluePrint has shown their utility in predicting the probability of a pCR after NCT in HR+, HER2- EBC.

In the FLEX data set, clinical factors and tumor grading alone were not able to differentiate patients between MammaPrint High 1 and High 2 tumors.
Both MammaPrint High 1 and High 2, show a response to chemotherapy. However, High 2 tumors have a significantly higher chemosensitivity than High 1 tumors.

The lower proportion of MammaPrint High 2 in Dutch routine testing is likely a result of a lower baseline clinical risk that is generally observed in a patient group primarily treated in the adjuvant setting, versus a cohort that is entirely treated in the neoadjuvant setting, as was also observed in the High 1 versus High 2 analysis of FLEX in a subgroup treated only in the adjuvant setting6.

These findings are relevant for cases identified with a MammaPrint High 2 tumor and a first indication in what the MammaPrint High 1 versus High 2 risk categories could contribute to MammaPrint-guided treatment decision making in the Netherlands.