Use of tamoxifen and aromatase inhibitors in a large population-based cohort of women with breast cancer

BACKGROUND: Non-compliance with oral treatment in oncology is an emerging health issue. For breast cancer (BC) patients, few data are available on compliance and persistence to tamoxifen in younger women and to aromatase inhibitors (AIs) as compared with tamoxifen in older women. METHODS: We constituted a cohort of 13 479 women with BC who received at least one prescription of tamoxifen or AI between 1998 and 2008, in the United Kingdom General Practice Research Database. Days covered by medication and treatment discontinuation were studied. Time to treatment discontinuation was calculated using Kaplan–Meier estimates. RESULTS: Overall, 18.9% (95% CI: 15.1–23.0) of women on AIs as compared with 31.0% (95% CI: 29.6–32.2) of women on tamoxifen had discontinued their treatments within the first 5 years (P<0.001). This rate raised to 50.7% (95% CI: 43.0–57.9) among the 416 women under 40 years receiving tamoxifen as initial hormonal therapy. Among older women, treatment discontinuation was less frequent for AIs as compared with tamoxifen (P<0.001). Among women on AI therapy, 14% of them (n=374) had switched treatments. CONCLUSION: Among older women, the real-life patterns of use of AI show high rates of compliance. In younger women, tamoxifen is prematurely discontinued for half of patients.