A molecular test can predict both risk for recurrence of breast cancer and likelihood of success with chemotherapy for the generally low-risk group of patients with estrogen-dependent, node-negative disease, according to an article in the December 30th issue of the New England Journal of Medicine.

The test measures levels of expression of a panel of cancer-related genes, and it was developed by researchers who used tissue samples and medical records from a trial of tamoxifen. Using fixed-tissue samples from 447 patients and a collection of 250 genes in three independent preliminary studies, 16 cancer-related genes were found that worked best. The scientists created a formula that generates a "recurrence score" based on the expression patterns in a tumor sample (range, 1-100).

Using biopsy tissue and medical records from another tamoxifen trial, researchers
divided 668 women into low, intermediate, and high risk of recurrence groups. Fifty-one percent were in the low risk group (with a score of less than 18); 22 percent were at intermediate risk (recurrence score 18 or higher but less than 31) group; and 27 percent were at high risk (a score of 31 or higher).

These risk group divisions correlated well with the actual rates of recurrence of breast cancer after 10 years. There was a significant difference in recurrence rates between women in the low and high risk groups. In the low risk group, there was a 6.8 percent rate of recurrence at 10 years; in the intermediate and high risk categories these rates were 14.3 and 30.5 percent, respectively. Up to a recurrence score of 50, rates of recurrence increased continuously as the recurrence score increased. These trends held across age groups and tumor size.