A breast cancer gene signature for indolent disease.

We describe a new ultralow risk threshold for the 70-gene signature (MammaPrint) that identifies a group of breast cancer patients with excellent 20 year, long-term survival prognosis. Tumors of these patients are referred to as "indolent breast cancer." We used patient series on which we previously established and assessed the 70-gene signature high-low risk threshold.

Our data indicate that patients with indolent disease may be candidates for limited treatment with adjuvant endocrine therapy based on their very low risk of distant recurrences or death of breast cancer.

In an independent validation cohort, we show that patients with indolent breast cancer had 100% breast cancer-specific survival at 15 years of follow-up.

Early-stage hormone-receptor positive breast cancer is treated with endocrine therapy and the recommended duration of these treatments has increased over time. While endocrine therapy is considered less of a burden to patients compared to chemotherapy, long-term adherence may be low due to potential adverse side effects as well as compliance fatigue. It is of high clinical utility to identify subgroups of breast cancer patients who may have excellent long-term survival without or with limited duration of endocrine therapy to aid in personalizing endocrine treatment.