Adherence to hormone therapy in a chemoprevention randomised trial

Background

Nonadherence to oral medication exists amongst women with breast cancer [1] and those participating in randomised clinical trials [2]. There is also evidence to suggest that nonadherence is more prevalent in chemoprevention trials than in adjuvant trials, with between 20% and 46% of patients in chemoprevention trials not adhering to medication [3]. The purpose of this study is to examine adherence amongst a subgroup of women participating in the International Breast Cancer Intervention Study (IBIS II) cognitive subprotocol. IBIS II is a randomised double-blind chemoprevention clinical trial of anastrozole versus placebo in postmenopausal women at high risk of breast cancer.

Methods

Two hundred and seven women participating in the cognitive subprotocol of the IBIS II trial are having cognitive and quality-of-life assessments conducted at three time points (prior to receiving the trial tablets, at 6 months and at 24 months post randomisation). Following the final assessment, a short semi-structured interview is conducted to elicit information regarding trial medication-taking behaviours.

Results

Fifty-three out of 207 women who participated in the IBIS II cognitive substudy had dropped out by 24 months (primarily due to side effects) and adherence data on 124 women who had a final assessment have been collected and are reported here. Seventy-one per cent (89 participants) were taking allopathic medication aside from the trial tablets, and 47% (58/124) were also taking supplements, for example multivitamins, ginkgo biloba, omega 3, and glucosamine. The total number of tablets taken a day ranged from 1 to 14, with a mean of 4.8 tablets per day. Only 15 women said they had ever experienced difficulty swallowing tablets and 10 of those were taking medication aside from the trial tablets. When participants were asked to indicate whether they had ever forgotten to take their trial tablets 50% (62 participants) said yes, but 37% (46 participants) stated only rarely. When asked whether participants ever chose not to take their trial tablets, for whatever reason, only 6/124 (5%) reported occasions when they had done so. Reasons included going away for holiday, not wanting to mix it with painkillers, and stomach upsets. When asked whether taking the trial tablets interfered with their daily life, the majority (90%, 111 participants) said never.

Conclusion

Adherence data from the IBIS II trial participants contrast with those found in the first IBIS trial (tamoxifen versus placebo). Early indications are that, contrary to previous findings, women receiving an aromatase inhibitor to prevent breast cancer appear on self-report to have little problem with daily tablet taking during the first 2 years of this 5-year clinical trial. Reasons for the differences may be due to sampling; women participating in the cognitive substudy may be a more motivated group, and it should be noted that almost one-third of women who dropped out did so because of vasomotor symptoms. Further monitoring of this group over a longer period is warranted.