Introduction
hormone receptor-positive breast cancer, cancer relapse [In postmenopausal women, cancers, breast cancer
CANCERS, RECURRENCE, BREAST CANCER RECURRENT, BREAST CANCER
Hormone receptor-positive [i.e., estrogen (ER) and/or progesterone (PR) receptor-positive] cancers account for 75 percent of all breast cancer cases. Adjuvant endocrine therapy blocks ER function or lowers estrogen levels, reduces the risk of recurrence, and improves survival among women with hormone receptor-positive early breast cancer.Aromatase inhibitors (AIs) suppress plasma estrogen levels by inhibiting peripheral conversion of androgens to estrogens and reduce breast cancer recurrence and mortality. AIs are the preferred adjuvant therapy for postmenopausal women with hormone receptor-positive breast cancer [Adjuvant AI treatment is often recommended for five to ten years according to the risk of cancer relapse [In postmenopausal women, levels of circulating E2 are typically within the range of 10 to 60 pmol/L [The primary aim of the present study was to analyze the effects of letrozole treatment on serum estrogens, especially E2, in postmenopausal breast cancer patients, using a highly sensitive and specific LC–MS/MS method. The aim was also to assess our routine chemiluminescent E2 method for monitoring of serum estradiol in post-menopausal patients and compare it to our sensitive LC–MS/MS. Secondary objectives were to analyze the effects of letrozole on serum E1 and to investigate the impact of baseline demographics, E2, E1, and FSH on QoL and treatment tolerability during adjuvant letrozole treatment.