ESMO Congress 2024 | OncologyPRO

Abstract 286P

Background

Although 5-year is recommended for adjuvant endocrine therapy (AET) for breast cancer patients, discontinuation of AET is common. We investigated the effect of early discontinuation to AET on patient survival.

Methods

We identified all female patients diagnosed with non-metastatic primary breast cancer during 2010-2015 who were aged 50 to 80 years with positive estrogen receptor (ER+) and underwent surgery in Alberta, Canada. To account for AET discontinuation due to palliative care, patients experienced recurrence or death within 6-month of AET discontinuation were categorized as AET adherent. Multivariate Cox regression was used to evaluate the effect of AET on survival, adjusting for patient and tumour characteristics including age tumour grade, stage, comorbidity.

Results

A total of 6930 patients were identified with a median age 63 years (IQR: 56-70). 85% of patients had positive progesterone receptor, and 90% were stage I or II. 1391 (20.1%) patients did not get AET, 3669 (52.9%) patients discontinued AET within 5 years (non-adherence), and 1870 (27.0%) patients were AET adherent. In non-adherence group, Tamoxifen, Aromatase Inhibitors (AIs) and both were prescribed to 43%, had, 29.0% and 28.0% patients, respectively. Compared to the no-AET group, both the non-adherence and adherence group had lower hazard ratios (HR) of 0.73 (95%CI: 0.63-0.84) and 0.76 (95%CI: 0.65-0.89) for recurrence-free survival (RFS), respectively, and 0.59 (95%CI: 0.51-0.69) and 0.52 (95%CI: 0.44-0.62) for overall survival (OS), respectively. Multivariate analysis also indicated improved HR in non-adherence group (RFS: 0.56, 95%CI: 0.48-0.66; OS: 0.48, 95%CI: 0.41-0.57) and adherence group (RFS: 0.55, 95%CI: 0.46-0.65; OS: 0.40, 95%CI: 0.33-0.49). Progesterone receptor positive was associated with a lower HR of 0.70 (95%CI: 0.54-0.91) for breast cancer specific survival (BCSS), and comorbidity was associated with higher HR for RFS and OS, but not BCSS.