Less than half of early-stage breast cancer patients with hormone-sensitive disease completed the full dose and schedule of their hormonal therapy treatment. These findings were recently published in the Journal of Clinical Oncology.
The majority of breast cancers are hormone receptor-positive. These cancers are stimulated to grow by the circulating female hormones estrogen and/or progesterone. Treatment of hormone receptor-positive breast cancer often involves hormonal therapies that suppress or block the action of estrogen. These therapies include tamoxifen as well as agents known as aromatase inhibitors. Tamoxifen acts by blocking estrogen receptors, whereas aromatase inhibitors suppress the production of estrogen in postmenopausal women.
Possible side effects of aromatase inhibitors include joint pain and decreased bone density. Tamoxifen is associated with some side effects similar to symptoms of menopause, which include hot flashes, irregular menstrual periods and vaginal discharge or bleeding. Not all women will experience these symptoms. More serious side effects can also occur as a result of long-term use of tamoxifen. There is a small increase in the number of blood clots in individuals taking tamoxifen. Individuals taking tamoxifen have a slightly increased risk of developing cataracts. In addition, tamoxifen appears to increase a woman’s risk of developing uterine cancer by about two- to three-times that of the general population.
Due to the duration of treatment with adjuvant hormonal therapy as well as possible side effects of treatment, patient adherence and continuation of therapy for the full duration can be challenging. According to the results of a study conducted in Ireland, many women who begin taking tamoxifen for the adjuvant treatment of breast cancer discontinue use (without switching to another hormonal therapy) before completing five years of treatment. In this study, older and younger patients were more likely to discontinue treatment as well as patients with additional health problems. Results from another study indicated that noncompliance with tamoxifen is common and results in significantly increased risk of recurrence. Medication adherence is very important in order to reduce risk of cancer recurrence or mortality. Researchers recently conducted a study in early-stage breast cancer patients receiving tamoxifen and/or an aromatase inhibitor in order to better understand adherence and continuation issues in this patient population.
In the current study, researchers evaluated pharmacy records of 8,769 Stage I-III hormone-sensitive breast cancer patients. Forty-three percent were undergoing hormonal therapy with tamoxifen, 26% with an aromatase inhibitor, and 30% with both tamoxifen and an aromatase inhibitor (sequentially). From the pharmacy records, hormonal therapy prescriptions and dates of refill were analyzed in order to determine rates of therapy discontinuation and adherence. The researchers were also able to analyze factors associated with suboptimal hormonal therapy dose or schedule from the pharmacy data. Of the 8,769 patients evaluated in this study, only 49% completed adjuvant hormonal therapy at the full dose and schedule. Factors associated with stopping treatment early included younger or older age as well as the presence of additional medical problems (comorbidites). Lumpectomy versus mastectomy was also associated with stopping treatment early. Factors associated with completing therapy included Asian race and being married. Treatment with chemotherapy and radiation in addition to hormonal therapy was also associated with completing hormonal therapy.
These researchers concluded that “interventions to improve adherence and continuation of hormonal therapy are needed, especially for younger women.” This study confirms findings of other studies evaluating hormonal therapy adherence issues. Strategies to improve patient adherence to treatment schedules and doses are critical to improve recurrence rates, especially for oral therapy like adjuvant hormonal therapy. It is critical for breast cancer patients who are undergoing treatment with adjuvant hormonal therapy to understand the risks and benefits of treatments as well as to understand the risks of stopping treatment early.
 Hershman DL, Kushi LH, Shao T, et al. Early Discontinuation and Nonadherence to Adjuvant Hormonal Therapy in a Cohort of 8,769 Early-Stage Breast Cancer Patients. Journal of Clinical Oncology. [early online publication]. June 28, 2010.