In a comparison of three methods for predicting the risk of recurrence in women treated for estrogen receptor (ER) positive breast cancer, only the breast cancer index (BCI), a biomarker based on expression levels of seven tumor specific genes, could accurately identify patients who continued to be at risk after five years of treatment with either tamoxifen or anastrozole.

“We have validated a unique fingerprint in the primary tumor of breast cancer patients that can help identify a high or low risk of cancer recurrence,” says study co-author Paul Goss, MD, PhD, director of the Breast Cancer Research Program at Massachusetts General Hospital Cancer Center.  “This should enable us to offer prolonged treatment to patients who remain at risk and, importantly, to avoid the costs and side effects of treatment in those at low risk.”

Standard treatment for early stage ER positive breast cancer includes fives years of treatment with either tamoxifen or an aromatase inhibitor that blocks the action of estrogen. The approach is sufficient in most patients, but some continue to experience recurrences in later years. The authors of the study noted that knowing whether or not a patient continues to be at risk is essential for determining if prolonged treatment is necessary.

The study, led by Sgroi, MD, of the MGH Cancer Center and Department of Pathology, was designed to compare the ability of the BCI in predicting long term recurrence risk with two other gene expression signatures that can predict risk within the first five years, the Oncotype Dx and the ICH4. All three methods were primarily used to analyze tumor samples from more than 650 study participants in a clinical trial comparing tamoxifen and anastrozole. Results were compared with patient records to determine individual rates of recurrence for up to 10 years after first surgical treatment.

All three methods could accurately predict recurrence during the first five years, but only the BCI was able to assess long term risk. The BCI was able to clearly distinguish 60 percent of patients whose risk was low from 40 percent who were at a significantly higher long term risk.

“We know that more than half the instances of recurrence in ER-positive breast cancer occur after five years of therapy with tamoxifen or anastrozole, so these findings are highly relevant to clinical management,” says Sgroi.  “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.”

This comparison study was published online in the journal Lancet Oncology.