Misattributing age-related symptoms to prophylactic tamoxifen may reduce adherence
medwireNews: Some symptoms experienced during preventive tamoxifen therapy and attributed to the medication could be age-related menopausal changes, say researchers who found an association between experiencing such symptoms early during treatment and reduced long-term adherence.
Using data on 3823 UK participants of IBIS (International Breast Cancer Intervention Study)-1, which randomly assigned women with an increased breast cancer risk to prophylactic tamoxifen 20 mg/day or placebo for 5 years, the team found no significant difference between treatment arms with respect to the effect of symptoms, such as hot flashes or nausea and vomiting, on adherence.
This finding indicates that “[w]omen may therefore be attributing age-related symptoms to their assigned medication,” and “is suggestive of the nocebo response, whereby seemingly inert substances cause adverse symptoms or effects,” the researchers write in the Journal of Clinical Oncology.
On the whole, over two-thirds of participants in either study arm adhered to the assigned treatment, defined as persistent use for at least 4.5 years, but the overall adherence rate was significantly lower in the tamoxifen than placebo arm, at 66.8% and 75.2%, respectively.
Experiencing certain predefined symptoms was associated with reduced adherence in both arms.
For instance, nausea and vomiting was significantly associated with reduced adherence in both the tamoxifen and placebo trials arms, with corresponding odds ratios (ORs) of 0.57 and 0.58, whereas gynecologic symptoms were linked to decreased adherence only among tamoxifen-treated women and headaches only among those given placebo, with ORs of 0.77 and 0.62, respectively.
For all symptoms evaluated in the study, with the exception of headaches, there was a significant association between increasing severity and lower adherence.
Other factors associated with nonadherence in multivariate analysis adjusting for confounders included tamoxifen use (OR=0.67), the presence of baseline menopausal symptoms (OR=0.73), current or ex-smoking status (OR=0.57 and 0.82, respectively), and baseline and prior use of hormone replacement therapy (OR=0.81 and 0.67, respectively).
By contrast, the likelihood of adherence was higher for premenopausal women (OR=1.29) and those who were older (OR=1.03 per year) or had a higher Tyrer-Cuzick 10-year breast cancer risk score (OR=1.03 per 1% increase).
Researcher Samuel George Smith (University of Leeds, UK) and colleagues conclude: “Our data have implications for communicating with prospective users of preventive therapy, particularly with regard to encouraging accurate symptom expectations and correcting potential misattributions.
“Intervention strategies are needed to promote adherence, as well as to effectively communicate the harms and benefits of preventive therapy to participants.”
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