Prognostic relation of body mass index on extended aromatase inhibition treatment in postmenopausal patients with estrogen receptor positive breast cancer: A retrospective analysis of the SOLE trial.

Background: Obesity is associated with a greater risk of developing distant recurrences in patients with estrogen receptor-positive (ER+) breast cancer. This association is however poorly investigated in patients treated with extended endocrine treatment (ET). We therefore evaluated the prognostic role of BMI in the SOLE trial, where postmenopausal patients, after having completed 4-6 years of adjuvant ET, were treated with 5 additional years of continuous or intermittent letrozole.

Patients & Methods: We considered the 3606 patients with ER+ /HER2- lymph node-positive BC with available BMI from the SOLE trial (NCT00553410). Distant-recurrence free interval (DRFI) was the main endpoint, and breast cancer-free interval (BCFI), disease-free survival (DFS) and overall survival (OS) secondary endpoints. Adjusted risk ratios (RR) for distant metastases were estimated with crude cumulative incidence models.

Results: 38.6 % of the patients were underweight or normal weight, 36.5 % overweight and 24.9 % obese. BMI was associated with age, tumor size, number of positive lymph nodes, menopausal status and type of prior ET. In the adjusted analyses, the prognostic value of BMI was dependent on prior ET and extended ET arm (second-order interaction p-value<0.001 for DRFI, BCFI and DFS, but not for OS). For instance, in patients treated with both a selective estrogen receptor modulator and an aromatase inhibitor in the first five years, obesity, as compared to normal-weight, was associated with better (RR=0.61, 95 %CI: 0.42-0.90) and worse (RR=2.31, 95 %CI: 1.41-3.78) outcomes in the adjusted models, in patients treated with continuous and intermittent letrozole in the extended ET, respectively.

Conclusion: We observed that the prognostic relation of BMI changes according to the type of adjuvant ET and mode of administration of extended AI. This warrants further investigation.