Compliance to adjuvant endocrine therapy and survival in breast cancer patients

Data on compliance to adjuvant endocrine treatment (ET) is mainly reported from prospective clinical trials or from smaller retrospective cohorts without correlation to outcome.

To determine compliance to adjuvant ET and the impact on survival in a population-based series of patients with early breast cancer (BC) advised ET.

1090 consecutive patients with hormone receptor positive (HR+) stage I-III BC diagnosed from 1 January 1997 to 31 December 2003 from one health care region of Sweden were included. Data on tumour, type of ET, compliance, reason for termination and outcome were collected. Statistical analyses were calculated with patients in three groups.

72 patients were excluded leaving 1018 patients with a HR+ stage I to III BC for analyses. The most common ET was tamoxifen (n = 751, 73.8%). At the last follow up (31 Dec 2019) with a median follow-up of 18 years (interquartile range 16-22) 228 (22.4%) patients had a relapse. 71.1% of the included patients were compliant to endocrine therapy. Older patients ≥74 years had lower compliance, 61% compared with 75% in the other age groups (≤50 years and 51-73 years) (p < 0001), other parameters including type of ET were not associated with compliance. Low compliance remained as an independent risk factor in multivariate analyses for lower relapse-free survival, HR=1.83, 95% Confidence Interval (CI) 1.52-2.19, p < 0.001 and for time to BC death, HR=2.69, 95%CI 1.82-3.98, p < 0.001.

Patients compliant to adjuvant ET have an improved survival.