Women going through menopause who experience symptoms like nausea or vomiting, and headaches, are much less likely to remain on preventive treatment for breast cancer than those who did not, even if they are at higher risk of this cancer, according to data from the International Breast Cancer Intervention Study I (IBIS-I).
The findings, recently presented at the 2016 San Antonio Breast Cancer Symposium, suggest that women may attribute menopausal symptoms to their medication — irrespective of being assigned tamoxifen of placebo — and are significantly less likely to adhere to their medication 4.5 years following treatment initiation.
The International Breast Cancer Intervention Study I (IBIS-I) investigated the use of tamoxifen in preventing breast cancer in women at risk of developing the disease. Tamoxifen, marketed under the brand name Nolvadex, among others, is a medication widely used both to treat breast cancer patients and as a preventive measure for people at increased risk of the disease.
Results of the study, which recruited 7,154 women from 36 centers in nine countries, showed that tamoxifen treatment for five years reduced the incidence of breast cancer by one-third in high-risk women.
“Data from the IBIS-1 and other trials indicate that five years of tamoxifen treatment reduces risk of breast cancer by at least 30 percent for women at increased risk for the disease, and that this effect seems to last for at least 20 years,” Samuel G. Smith, PhD, a Cancer Research UK postdoctoral fellow and university academic fellow at the University of Leeds, said in a news release. “However, the effectiveness of tamoxifen is dependent on its appropriate use for the duration of therapy.”
Researchers looked into data from the IBIS-I study to assess the effects of menopausal symptoms on treatment adherence. Their analysis focused particularly on the 3,987 women in the U.K. who were included in the study, 2,000 of whom were assigned to placebo while the remaining 1,987 received tamoxifen.
Results showed that significantly more women who received the placebo remained adherent to the medication for at least 4.5 years, compared to the tamoxifen-treated group (71.5% vs 62.1%).
Regarding side effects, 5% of all women taking part in the study reported nausea or vomiting, 7% reported headaches, 31.5% hot flashes, and 13.8% gynecological symptoms, such as vaginal dryness and irregular bleeding.
Importantly, patients on the placebo and tamoxifen arms who said they had experienced nausea and vomiting were 82% and 84% more likely to be nonadherent to their therapy, respectively, that those who did not report such symptoms.
In the placebo group only, those reporting headaches were significantly (70%) more likely to be nonadherent. Gynecological symptoms, in contrast, were associated with adherence to medication only in the tamoxifen group, and led to 30% of these women stopping treatment.
“We were surprised to find that while menopausal symptoms do play a role in adherence to medication, the strength of the association between menopausal symptoms and adherence was similar among those women assigned placebo and those assigned tamoxifen,” Smith said. “This suggests that women may be attributing menopausal symptoms that occur naturally as being caused by the medication that they are taking. Therefore, we need to find new and innovative ways of supporting women who experience these symptoms.”
Specifically, he said, “Our findings have implications for how clinicians communicate with women who are considering initiating breast cancer preventive therapy. Managing expectations, and providing realistic and accurate information about the likelihood of experiencing a side effect, as opposed to a naturally occurring symptom, is needed.”
The researchers reported that their study had some limitations, including the fact that adherence was assessed during routine clinic visits, so the accuracy of stated adherence is not certain. “This is a problem in all medication adherence studies, and a gold standard assessment needs to be developed,” said Smith.