A biomarker based on the expression levels of seven tumor-specific genes was able to accurately assess the risk for breast cancer recurrence beyond the first 5 years of treatment. This knowledge can help clinicians identify which patients would benefit from prolonged estrogen inhibition.

The breast cancer index (BCI) assay combines two biomarkers for recurrence risk assessment: the molecular grade index, which measures expression levels of five genes related to tumor proliferation, and the H/I ratio, which compares expression levels of two other genes. All three tests were developed by researchers from Massachusetts General Hospital (MGH) in Boston, Massachusetts, in collaboration with bioTheranostics, Inc.,  San Diego, California.

A team led by Professor Dennis C. Sgroi, MD, of the MGH Cancer Center and the MGH Department of Pathology, compared the prognostic ability of the BCI assay, the 21-gene recurrence score (Oncotype DX® breast cancer assay), and an immunohistochemical prognostic model (IHC4) for both early and late recurrence in patients with estrogen receptor (ER)-positive, node-negative  breast cancer. All participants had taken part in the Arimidex, Tamoxifen, Alone or in Combination (ATAC) trial. Standard treatment for early-stage, ER-positive breast cancer includes 5 years of treatment with either tamoxifen or an aromatase inhibitor, such as Arimidex (anastrozole).

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Suitable tissue for BCI analysis was available from 665 patients. Sgroi and colleagues reported in The Lancet Oncology (2013;14[11]:1067-1076) that all three assays demonstrated significant prognostic ability for early distant recurrence (recurrence in the first 5 years). However, only the BCI had significant prognostic ability for late distant recurrence (recurrence 5 to 10 years later). As noted in an MGH statement, the BCI could clearly distinguish the 60% of patients with very low risk from the 40% who continued to be at significant long-term risk.

“We know that more than half of instances of recurrence in ER-positive breast cancer occur after 5 years of therapy with tamoxifen or anastrozole, so these findings are highly relevant to clinical management,” explained Sgroi in the MGH statement. “Since the BCI identifies two distinct risk groups, it may provide a much-needed tool in determining those patients who need extended hormonal therapy and those who may be spared its well-known adverse side effects.”