A breast cancer patient's survival could depend on how his or her genetic makeup inhibits the effect of certain chemotherapy treatments including cyclophosphamide, according to a study of some 590 women in Norway and the U.S. A specific variant in the SOD2 gene that produces an important protein guarding against cellular damage from free radicals may lessen the effect of some breast cancer drug therapies.

This variant modifies the function and structure of the MnSOD enzyme (that typically protects cells from damage created by reactive oxygen species that form during cellular metabolism). Previous research has found this enzyme's ability to neutralize these reactive oxygen species may affect the action of some chemotherapy drugs.

This latest study observed the effect of this variation on the survival rates of breast cancer patients who underwent chemotherapy as compared to those who didn't. Although two forms of chemotherapy worsened a female's survival, the presence of the SOD2 gene had no effect on the lifespan of patients receiving no chemo at all. In addition, three different kinds of common chemotherapy drugs also affected the survival rates of breast cancer patients with the SOD2 variant negatively.

Researchers anticipate the development of tests to assist doctors in screening for these variations and targeting safer, more effective chemotherapy strategies.

Clinical Cancer Research, Vol. 15, No. 12, p. 4165-4173, June 15, 2009

Cancer.gov June 9, 2009

Cyclophosphamide (Cytoxan) is a trademark of Micromedex.

Image source: National Cancer Institute