Comparing the two groups might help explain why some estrogen-receptor-positive breast cancer patients do well with estrogen-lowering drugs and others poorly.

Reporting in Nature Genetics, researchers said genetic variants on chromosome 2 and on chromosome 16 May increase the risk of estrogen-receptor-positive breast cancer.

Female mice that lacked an estrogen receptor were born with longer digits, and those that did not have testosterone had shorter, superfeminine digits.