SAN ANTONIO – Women who experienced menopause-related nausea/vomiting and headaches were significantly less likely to adhere to their assigned medication 5 years after initiating therapy, according to a study presented at the 2016 San Antonio Breast Cancer Symposium (SABCS).1

The placebo-controlled, randomized International Breast Cancer Intervention Study I (IBIS-I) evaluated whether 5 years of tamixofen treatment was superior to placebo for reducing breast cancer recurrence.

“Data from the IBIS-1 and other trials indicate that 5 years of tamoxifen treatment reduces the risk of breast cancer by at least 30% for women at an increased risk for the disease, and that this effect seems to last for at least 20 years,” said Samuel G. Smith, PhD, Cancer Research UK postdoctoral fellow and university academic fellow at the University of Leeds in the United Kingdom. “However, the effectiveness of tamoxifen is dependent on its appropriate use for the duration of therapy.”

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Therefore, researchers sought to assess the impact of menopausal symptoms on adherence to treatment among 3987 women from the United Kingdom enrolled in the IBIS-I trial, of which 2000 were assigned to placebo and 1987 were given tamoxifen.

Results showed that patients receiving placebo were 53% more likely to be adherent to therapy compared with those who received placebo (odds ratio [OR], 1.53; 95% CI, 1.34-1.75; P < .0001).

In addition, researchers found that 5.0%, 7.0%, 31.5%, and 20.9% experienced nausea/vomiting, headache, hot flashes, and gynecologic symptoms, respectively, with most cases being mild.

The study demonstrated that women who experienced nausea/vomiting were 82% (OR, 1.82; 95% CI, 1.16-2.87; P = .009) and 84% (OR, 1.84; 95% CI, 1.22-2.76; P = .004) more likely to be nonadherent to placebo and tamoxifen, respectively, compared with women who did not report these symptoms. Similarly, patients in the placebo arm who reported headaches were 70% more likely to be nonadherent to therapy (OR, 1.70; 95% CI, 1.16-2.50; P = .006).

Gynecological symptoms were significantly associated with adherence only in the tamoxifen arm, with those reporting this symptom 30% more likely to be nonadherent (OR, 1.30; 95% CI, 1.05-1.63; P =.02). Hot flashes were not significantly associated with adherence in either treatment arm.

“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,” Dr Smith continued. “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.”


1. Smith SG, Sestak I, Forbes J, Howell A, Cuznick JJ. Menopausal symptoms as predictors of long-term adherence in the International breast cancer intervention study (IBIS-1). Paper presented at: 2016 San Antonio Breast Cancer Symposium; December 6-10, 2016; San Antonio, TX.