Endocrine effects of adjuvant letrozole versus tamoxifen in hormone responsive postmenopausal early breast cancer patients: results from the HOBOE randomized trial.

Abstract

Abstract Abstract #1150 Purpose. We compared the endocrine effects of 6 and 12 months of adjuvant letrozole versus tamoxifen in postmenopausal patients with hormone responsive early breast cancer, within an ongoing phase 3 trial (HOrmonal adjuvant treatment BOne Effects – HOBOE, ClinicalTrial.gov id: NCT00412022).
 Patients and Methods. Patients were randomised to receive tamoxifen or letrozole ± zoledronate. Serum values of 17-b-estradiol, FSH, LH, testosterone, dehydroepiandrosterone-solphate, progesterone, and cortisol were measured at baseline, after 6 and 12 months of treatment. For each hormone, baseline, 6 and 12-month values were compared between treatment groups, by the exact Wilcoxon-Mann-Whitney test.
 Results. At December 31, 2006, 157 postmenopausal patients had been enrolled into the study; baseline data were available for 139 patients (88.5%), 43 assigned to tamoxifen and 96 assigned to letrozole. Median age was 61 and 62 years in the two groups, respectively. Baseline values were similar between the two groups for all hormones. At 6 and 12 months, levels of 17-b-estradiol were significantly lower with letrozole as compared with tamoxifen (p=0.0003 and p<0.0001, respectively). Patients treated with letrozole also showed higher levels of progesterone and testosterone at 6 (p=0.001 and p=0.01, respectively) and 12 months (p=0.004 and p=0.02, respectively) than those treated with tamoxifen. FSH and LH were lower (all p<0.0001 for both hormones), while cortisol was higher (p=0.003 at 6 and 0.001 at 12 months) with tamoxifen than with letrozole.
 Conclusion. To our knowledge, this is the first study reporting on endocrine effects of letrozole as adjuvant treatment of postmenopausal early breast cancer and allowing a prospective comparison with tamoxifen. Adjuvant letrozole and tamoxifen result in significantly distinct endocrine effects. Such differences can explain the higher efficacy of letrozole as compared to tamoxifen. Long-term impact needs to be studied. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 1150.