Adjuvant tamoxifen is widely used as endocrine treatment for oestrogen receptor positive (ER+) breast cancers (BC). Guidelines recommend the use of tamoxifen up to 10 years. Tamoxifen can cause serious side effects and not all patients need adjuvant tamoxifen to have an excellent prognosis. To avoid overtreatment, a test that identifies these patients is necessary.

The 70-gene FDA-approved MammaPrint has potential to select patients that have an excellent survival without chemotherapy and only limited or no tamoxifen treatment.
Three thresholds are predefined and indicate the expected benefit of tamoxifen and chemotherapy.[1,2]

Aim

To validate whether the MammaPrint ultralow threshold can select postmenopausal BC patients with an excellent prognosis after only limited or no tamoxifen treatment.

Survival analysis

Recurrence Free Interval (RFI) was defined as time from the first randomization to the occurrence of a local, regional or distant recurrence or breast cancer‐specific death. Patients with a secondary con-tralateral breast tumor were censored at the time of the contralateral diagnosis. Median follow-up was 8 years for RFI and 13 year for overall survival (OS). Shown are the percentage of patients per group without an event at 10 years and the upper 95% confidence.

Conclusion

Postmenopausal node negative patients with an Ultralow MammaPrint score have an excellent RFI with ≤3 years of endocrine treatment.