Analysis of gene expression in post-surgery breast cancer has helped researchers identify which patients can bypass chemotherapy after surgery. A longer follow-up study will be needed to verify the results, but initial data published in the New England Journal of Medicine supports the clinical usefulness of the 21-gene assay (Oncotype DX Recurrance Score, Genomic Health), at least in a low-risk cohort of women.
The study, sponsored by the National Cancer Institute, was comprised of 10,253 women aged 18–75 years with axillary node-negative invasive breast cancer that was estrogen-receptor positive, progesterone-receptor positive, or both, and did not express epidermal growth factor receptor 2 (HER2). All participants of the study were assigned an Oncotype DX Recurrence Score. Those with a score between 0 and 10 were treated with endocrine therapy alone, and those with scores higher than 25 received both chemotherapy and endocrine therapy. Patients with scores between 11 and 25 were randomly assigned to endocrine therapy alone or endocrine therapy with chemotherapy. The study design was intended to confirm prior research that demonstrated the effectiveness of endocrine therapy alone in patients with scores lower than 11 and the superiority of adjuvant chemotherapy in those with scores between 26 and 30.
Over the 5-year study period, patients with scores between 1 and 10—who were treated with endocrine therapy alone—had <1% risk of breast cancer recurrence and <2% risks for any other type cancer recurrence. The high-risk patients (those with scores between 26 and 30) saw only a marginal benefit to risk of breast cancer recurrence and no effect on risk for recurrence of non-breast cancers.
The study shows a significant step forward in the use of Oncotype DX testing, which only costs about $4,000 and is covered by most insurers. Successful guidelines can help patients in the low risk group to avoid the burdensome and expensive side effects of chemotherapy while still maintaining strong survival outcomes. However, the team admits that more research will be required to optimize treatment for patients with scores between 11 and 25, a demographic that comprised over 67% of participants and who were still considered to have a moderate risk of relapse.
