MammaPrint® is a test that measures the activity of certain genes within tumour cells to estimate the likelihood of the tumour to return and spread to other organs, where it becomes incurable. Based on the outcome of MammaPrint®, depending whether the tumour has a low or high risk of returning and in consultation with the clinician, it can be determined whether or not additional chemotherapy is needed after surgery. This 'gene expression test' analyses the activity of 70 genes in the breast tumour and claims to be a tumour fingerprint.

One RCT (MINDACT) was identified [4]. MINDACT was an open-label, randomised controlled, phase 3 trial of women with early-stage breast cancer (n=6693, median follow-up five years). The investigators aimed to provide prospective evidence of the clinical utility of MammaPrint® added to standard clinicopathological risk assessment compared to standard clinicopathological risk assessment alone. MINDACT focused on discordant risk groups: a subgroup with a clinical high-risk profile discordant with a genomic low-risk profile (clinical high and genomic low; CH/GL) and a subgroup with a clinical low-risk profile discordant with a genomic high-risk profile (clinical low and genomic high; CL/GH). MINDACT's primary objective was to assess whether chemotherapy could be safely withheld in the CH/GL subgroup without affecting distant metastasis-free survival (DMFS). The authors predefined the cut-off for non-inferiority as the lower boundary of the 95% confidence interval (CI) of the five-year rate of DMFS should be more than 92% in CH/GL patients who did not receive chemotherapy based on the MammaPrint® result.

Based on the MINDACT it cannot be concluded that it is safe to omit chemotherapy, because the 95% CI's of all surrogate outcomes for ten-year OS (five-year DMFS, five-year DFS and five-year OS) are crossing the non-inferiority threshold (HR 0.80 and 3% risk difference). Even the results of five-year DFS indicate that MammaPrint® is possibly clinically relevant inferior in comparison with treatment based on AO!.