The side effects of endocrine therapy caused many breast cancer patients to forgo or stop taking drugs recommended for breast cancer expressing the hormones estrogen or progesterone.
About 75 percent of all breast cancers are estrogen dependent, meaning they grow in response to estrogen. Of those, 65 percent also grow in response to progesterone. Endocrine therapy for breast cancer helps prevent recurrence by blocking the effects of estrogen.
Two types of endocrine therapy, tamoxifen or aromatase inhibitors, have side effects that mimic symptoms of menopause, such as hot flashes and vaginal dryness. In addition, both drugs can cause joint pain.
University of Michigan researchers surveyed 743 women from Detroit and Los Angeles: 11 percent never started taking their prescribed drug while 25 percent stopped taking it early. The women were supposed to take a daily dosage of tamoxifen or aromatase inhibitors for five years to reduce cancer recurrence and increase survival. Recent studies suggest some women may benefit from continuing the therapy for 10 years.
Women who received less information about endocrine therapy were less likely to begin the treatment regimen. Likewise, women who saw a breast surgeon instead of a medical oncologist as their primary follow-up were less likely to begin the therapy. The research points to a need to better educate patients about benefits of endocrine therapy and its expected side effects.
Women more worried about their cancer recurring were more likely to finish the therapy, as were women who took medication regularly. The survey results were published in the March issue of Breast Cancer Research and Treatment.