Why a popular breast cancer drug may be less effective for some Africans

A gene mutation appears to impair tamoxifen’s ability to tackle the disease

Some round white pills sit beside a pill bottle labeled tamoxifen, which is a popular breast cancer drug.

Tamoxifen, a breast cancer drug, helps derail a strategy that cancer cells exploit to grow.

Bill Branson/National Cancer Institute

WASHINGTON — A genetic variant commonly found in some Africans may stymie the effects of a popular breast cancer drug.

The variant produces a sluggish version of the enzyme known to activate tamoxifen. People who inherit two copies of the variant show five times less active drug in their bloodstreams compared with people who don’t have that variant, researchers reported November 2 at the American Society of Human Genetics annual meeting.