From the article:
In the current nested case-control study, 153 WHEL [Healthy Eating and Living Study] participants whose cancer had recurred were matched with 153 participants who remained cancer-free. These pairs were alike in terms of tumor type, body size, age, ethnicity, use of chemotherapy and other variables. Two-thirds of the participants were using tamoxifen, Rock said.
When they enrolled, researchers tested the women’s blood for concentrations of the steroid hormones estradiol (the primary human estrogen) and testosterone. They analyzed different forms of estradiol and testosterone in the blood, such as how much was bound to transport proteins (such as to the sex hormone binding globulin, or SHBG) and how much was “free” circulating and able to enter a cell.
Researchers found that higher estradiol concentrations, in all forms, significantly predicted cancer recurrence. Overall, women whose cancer came back had an average total estradiol concentration that was more than double the average for women who remained cancer-free. Increased levels of testosterone or SHBG levels were not associated with recurrence, contradicting the findings of several previous studies.