46% of patients could be spared chemotherapy.

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The MINDACT trial sponsored and run by the European Organisation for Research and Treatment of Cancer  – involving 112 hospitals in 9 countries from 7 BIG collaborative groups – represents a large academic effort towards de-escalating therapies.The study was designed to evaluate the utility of adding the 70-gene test (MammaPrint) to the standard clinicopathological criteria used to identify those patients with early-stage breast cancer who could be safely spared adjuvant chemotherapy without this significantly affecting their risk of disease recurrence.

Between 2007 and 2011 the trial enrolled 6,693 women with node-negative or 1-to-3 node positive breast cancer.

46% of the patients identified as high-risk for cancer recurrence based on traditional factors were identified as low-risk when adding the MammaPrint test. Based on good outcome results without chemotherapy, the data suggested that chemotherapy provided no clinically meaningful benefit for these patients and could be safely omitted.

MINDACT gives hope to many women with node-negative or 1-to-3 node positive early breast cancer. The study’s results provide the highest level of evidence showing that Mammaprint could significantly de-escalate the use of adjuvant chemotherapy in the future, thereby improving the quality of life of a great many women confronted with the disease.

The primary results of MINDACT were published in 2016 in the New England Journal of Medicine. The updated results of MINDACT, published in March 2021 in the Lancet Oncology, with a median follow-up of 8.7 years supported the 2016 findings and confirm the clinical utility of MammaPrint® to identify patients with early breast cancer who may safely avoid post-surgery chemotherapy. While they show a slightly larger distant metastasis-free survival for the discordant c-High/g-Low group, the estimated gain of 2.6% for chemotherapy administration in these patients remains small in light of the harmful side effects of the chemotherapy.

The long-term follow-up analysis also included an exploratory analysis by age. The 70-gene signature test was shown to be particularly useful in decision-making for postmenopausal women within the c-High/g-Low group, for whom chemotherapy added no benefit. In younger women, chemotherapy may still add benefit, but this requires careful discussion between doctor and patient.