In some women, tamoxifen acts as an "anti-estrogen" agent to prolong survival and combat recurrence of types of breast cancer that are related to estrogen. However, the drug’s effectiveness has not been universal, prompting the scientists to look for a genetic difference in women who show less improvement in survival on tamoxifen therapy.

Their study involved 160 women who had received tamoxifen and another 177 women with breast cancer who had not. The women who did not receive the drug had similar survival rates regardless of whether they possessed the "slow version" of the gene, but the difference in responses was evident in women who received tamoxifen. Women who had inherited the "slow" gene from both parents were three times less likely to survive as women who had two normal SULT1A1 genes, or one "slow" and one normal gene. The scientists took into account age, ethnicity, and stage of tumor at diagnosis, finding that the genetic effect persisted even when those factors were considered.

Nowell and other scientists and physicians at the Arkansas Cancer Research Center next will recruit patients with new diagnoses of breast cancer, who are to receive tamoxifen therapy, for a long-term study of the effects of tamoxifen in women with and without the "slow" gene. Laura Hutchins, M.D., at the cancer center will recruit the patients for that study, which the U.S. Department of Defense will fund. Nowell holds a predoctoral fellowship with the U.S. Department of Defense Breast Cancer Research Program.