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Adjuvant endocrine therapy is recommended for all eligible patients with breast cancer for a minimum 5-year period. Durations of therapy for a shorter period have worse outcomes for patients. This study examined whether women in the community completed the full course of adjuvant endocrine therapy.
All women diagnosed and treated for breast cancer in the Tayside region of Scotland during the period January 1993 to December 2008 were identified. Information on dispensed prescribing was linked to hospital discharge records, breast cancer clinical audit, cancer registry and death certification for each individual. Patients were identified as starting either aromatase inhibitor (AI) or tamoxifen therapy and their dispensed prescribing analysed to see whether they completed a 5-year course.
A total of 5,729 women were identified with an incident cancer within the study. Seventy-one per cent were initially prescribed tamoxifen, 8% AIs and 21% received no adjuvant medication. Nineteen per cent of women started on tamoxifen switched treatments, compared with 25% starting AIs. For patients followed for at least 1 year, 51 (11%) started on AIs had stopped medication compared with 373 (9%) on tamoxifen. At year 2, an additional 40 (12%) stopped AIs and 384 (11%) tamoxifen. For 3-year follow-up, an additional 39 (19%) stopped AIs, while 351 (11%) stopped tamoxifen. For patients followed for at least 4 and 5 years, respectively, an additional 22 (26%) then 5 (20%) stopped AIs compared with 297 (11%) and 316 (16%) patients who stopped tamoxifen.
Large numbers of patients prescribed adjuvant endocrine therapy stop medication before completing the recommended 5-year period, with approximately 20% stopping in the first 2 years. This is likely to have a detrimental effect on patient outcomes. All patients need to be encouraged to continue their medication for the full 5-year recommended period to ensure they receive the maximum benefit.