Switching endocrine therapy in breast cancer as a strategy for musculoskeletal symptoms, tolerance, and adherence.

Abstract

192 Background: Adverse effects of endocrine therapy (ET), especially musculoskeletal symptoms (MSS), represent the major cause of treatment discontinuation in breast cancer (BC) patients, resulting in increased risk of recurrence. Aromatase inhibitors (AI), the mainstay of ET, are associated with a high incidence of MSS such as arthralgia and myalgia. The hypothesis of whether switching ET subclass improves adherence and symptoms was tested. Methods: We conducted a retrospective single site chart review of female patients with nonmetastatic BC, who were seen at Cancer Clinic from January to June of 2017. All patients received AI as a first choice of adjuvant ET; those with disease recurrence while on ET were excluded. We collected data on baseline health, adherence and discontinuation rate, as well as whether switching to a different ET agent (another AI or tamoxifen) was attempted. The subsequent compliance and symptomatology after switching were assessed. Results: 483 eligible patients were identified and divided into 4 groups based upon adherence: 354 (73.3%) were found to be compliant with AI without interruption, 109 (22.5%) switched to a different ET and remained compliant (≥ 1 switch), 16 (3.3%) eventually discontinued ET despite attempting ≥ 1 switch, and 5 patients (1.0%) stopped treatment without a switch. On comparison of the different groups, patients who permanently discontinued ET were more likely to be elderly and have preexisting musculoskeletal condition. MSS was found to be the single most common cause for AI intolerance (105 patients, 81.4%). The median time to switch was 6.3 months (0.3-63.9). Among the compliant switchers, most needed only 1 switch (79) but there were patients who required 2 or 3 switches (23 and 6, respectively). Majority of patients switched from anastrozole to exemestane (84, 51.8%). Significant improvement in symptoms after the switch was reported by 73.3% of patients. Conclusions: Switching between different ET subclasses is an effective treatment strategy to alleviate side effects and enhance adherence to ET. A higher compliance rate of 95.8% was observed in our study compared to a national average estimated at < 80%.