MINDACT

Background

Phase III prospective clinical utility trial. 6693 patients with early breast cancer (T1-2 or operable T3, N0-1) evaluated with both the 70-gene signature (MammaPrint) for genomic risk and a modified Adjuvant! Online clinical risk score. Patients with discordant clinical-high/genomic-low or clinical-low/genomic-high risk were randomized to receive or omit chemotherapy. Primary focus: can chemotherapy be safely omitted in clinical-high but genomic-low risk patients?

Interventions and follow up

Arm A: Clinical-high/genomic-low patients randomized to chemotherapy + endocrine therapy
Arm B: Clinical-high/genomic-low patients randomized to endocrine therapy alone (no chemotherapy)
Primary endpoint: 5-yr distant metastasis-free survival (DMFS) in clinical-high/genomic-low patients receiving no chemotherapy (non-inferiority)
mFollow up: 8 years

Results

5-yr DMFS (chemo omission, cH/gL): 94.7% vs 95.9% (no chemo vs chemo), difference -1.2%, 95% CI -3.0 to 0.5% — non-inferior (meets pre-specified margin)
8-yr DMFS (cH/gL): 92.0% vs 93.3% (no chemo vs chemo) — non-inferior
cL/gL (no chemo observational): 5-yr DMFS 97.6% — excellent outcome

Adverse events

Chemotherapy-related toxicity (avoided in no-chemo group): alopecia, nausea, myelosuppression, and secondary-malignancy risk avoided when chemotherapy was omitted
Quality of life: significantly better in the chemotherapy-omission group; no excess late toxicities in the no-chemotherapy arm

Conclusions

Patients with clinical-high/genomic-low risk early BC had non-inferior 5-yr DMFS when chemotherapy was omitted, supporting the use of the 70-gene signature (MammaPrint) to guide chemotherapy de-escalation in clinical-high-risk patients. Roughly 46% of enrolled patients had clinical-high/genomic-low risk, suggesting the assay could prevent overtreatment in a substantial proportion.

Key Limitations

The pre-specified -3% non-inferiority margin in 5-yr DMFS was met (observed -1.2%, 95% CI -3.0 to 0.5%), but the upper confidence bound still includes a clinically meaningful chemotherapy benefit for some patients. Premenopausal women showed a larger numerical chemotherapy benefit (possibly OFS-mediated) — subgroup caution warranted. Node-positive (N1) patients were enrolled and chemotherapy benefit in N1/cH/gL is debated. MammaPrint (MINDACT) and Oncotype DX (TAILORx) serve overlapping but distinct populations; guideline integration varies by region.

Clinical Context

MINDACT validated MammaPrint as a clinical tool to de-escalate chemotherapy in cH/gL patients. In US practice, Oncotype DX (TAILORx) is more widely used for N0 patients, while MammaPrint and Prosigna (PAM50) are more common in Europe; all are endorsed by ASCO and ESMO for specific indications. Genomic-risk-guided chemotherapy de-escalation has become standard, sparing chemotherapy in a substantial fraction of eligible patients. ESMO-MCBS: not applicable (clinical-utility/de-escalation trial).

References