Blood hormone levels predicted long-term breast cancer risk for postmenopausal women

"We found that a single hormone level was associated with breast cancer risk for at least 16 to 20 years among postmenopausal women not using postmenopausal hormones," said Xuehong Zhang, M.D., an epidemiologist at Brigham and Women's Hospital and an instructor in medicine at Harvard Medical School in Boston, Mass. "We, and others, are now evaluating if the addition of hormone levels to current risk prediction models can substantially improve our ability to identify high-risk women who would benefit from enhanced screening or chemoprevention. If so, the current data suggest that hormone levels would not need to be measured in the clinic more than once every 10, or possibly 20, years."

Zhang and colleagues analyzed 796 patients with postmenopausal breast cancer who had not received hormone therapy. They conducted blood hormone tests at two time points: between 1989 and 1990, and between 2000 and 2002. They then matched each patient with two controls who were not diagnosed with breast cancer.

Women with hormone levels in the highest 25 percent for estradiol, testosterone and dehydroepiandrosterone sulfate (DHEAS) had a 50 percent to 107 percent greater chance for developing breast cancer compared with women in the lowest 25 percent. Relative risks for developing breast cancer were similar at one to 10 years versus 11 to 20 years (also 16 to 20 years) after blood collection.

Zhang and colleagues also investigated whether these higher hormone levels were more closely linked to hormone receptor- (HR) positive breast cancers and if they predicted risk regardless of tumor aggressiveness.

In the first case, they found that elevated levels of estradiol increased a woman's risk for HR-positive breast cancer. In general, increased hormone levels, except for DHEAS, tracked closely with increased risk for HR-positive breast cancer. Data on HR-negative cancers were inconclusive.

Elevated hormone levels were also associated with aggressive breast cancer, which the study defined as recurrent or fatal cancer. "The relationship was comparable or possibly stronger for recurrent and fatal breast cancer than it was for overall breast cancer risk, although these results were based on relatively small numbers of participants," said Zhang.

Researchers also confirmed the protective effect of sex hormone-binding globulin (SHBG), which seems to negate the cancer-causing effects of certain hormones. Women in the highest 25 percent of SHBG levels had a 30 percent lower risk for breast cancer compared with women in the lowest 25 percent for SHBG levels.

Zhang noted that the study had low case numbers for several cancer subgroups, including HER2-positive, triple-negative and basal-like breast cancers. More research is necessary to determine the relationship between elevated hormone levels and these important breast cancer subtypes.