European doctors said Friday they had identified a genetic characteristic that strongly worsens survival chances for women with breast cancer who are treated with a common form of chemotherapy.
The telltale sign is a variant of a gene called NQO1, which in its normal form produces an enzyme that protects cells against oxidative stress -- a key factor in the spread of cancer.
The variant of NQ01, called NQ01*2, stops production of this protective enzyme. It is present in between four and 20 percent of the world's population, with a preponderance in Asia, according to figures presented in the study.
The researchers -- led by Heli Nevanlinna of the University of Helsinki and Jiri Bartek, a Czech scientist with the Danish Cancer Society -- found that women who had a double copy of NQ01*2 in their genome had only a 17-percent survival rate when treated with an anthracyclin-based chemotherapy.
Those who had only a single copy of NQ01*2, or did not have the variant at all, had a survival rate of 75 percent.
The paper, published online by the specialised British journal Nature Genetics, is based on DNA data from more than 2,000 Finnish women treated for breast cancer.