Cancer Research Lab

About one third of women with breast cancer who are prescribed tamoxifen stop taking the drug well before the end of the optimum 5 years of treatment, and thus jeopardize their chances for treatment success, Irish researchers report.

The discontinuation rate of tamoxifen treatment observed in current clinical practice is nearly twice that observed in controlled clinical trials, Dr. Thomas I. Barron and his associates report in the March 1st issue of Cancer. But clinical trials do not reflect “real-life” oncology practice, since patients tend to be carefully selected, highly motivated, and closely monitored, with adherence based on subjective self-reports.

Dr. Barron and associates at the St. James’ Hospital in Dublin evaluated tamoxifen adherence using a more objective measure of adherence — prescription refill data. Using the Irish Health Services pharmacy database, the researchers obtained information for 2816 women 35 years of age or older who initiated tamoxifen therapy between January 2001 and January 2004.

The investigators found the rates of nonadherance with tamoxifen discontinuation to be 11.1% by day 30; 14.5% by day 90; 22.1% by 1 year; and 28.4% by 2 years. By 3.5 years, 35.2% of patients had stopped using tamoxifen without switching to an alternative hormonal treatment.

The biggest risk factor for nonadherance, as expressed by a crude hazard ratio (HR) of 1.78, was cognitive or functional impairment, such as Parkinson’s disease or dementia. Extremes of age were also important: compared with women between 45 and 54 years old, the HR for those between 35 and 44 years and women older than 75 were 1.36 and 1.42, respectively.

These findings support suggestions that psychological problems may impair medication adherence, with HRs for antidepressant use of 1.31 and antipsychotic use of 1.16.

Even though interventions to improve adherence are costly and time-consuming, Dr. Barron and his team conclude that “their use may be worthwhile in oncology patients.”