Intermittent Letrozole Administration as Adjuvant Endocrine Therapy for Postmenopausal Women With Hormone Receptor-Positive Early Breast Cancer: A Biologic Study.

Background: Letrozole withdrawal for 3 months might permit estrogenic stimulation in residual resistant breast cancer disease susceptible to letrozole reintroduction. We investigated the impact of a 3-month letrozole-free interval on serum estradiol levels in patients with early stage breast cancer.

Patients And Methods: Postmenopausal women with estrogen receptor- and/or progesterone receptor-positive (> 10% of immunoreactive cells), node-negative early breast cancer were eligible. Patients received letrozole for 5 years with a 3-month treatment-free interval after the first year of therapy. The primary end point was to evaluate the increase in serum estradiol levels after a 3-month treatment-free interval. The secondary end points were the evaluations of other biologic markers (eg, follicle-stimulating hormone, luteinizing hormone, cholesterol, high-density lipoprotein, triglycerides, osteocalcin).

Results: From November 2007 to February 2012, 130 evaluable patients were enrolled. The median age was 61 years. Mean values of estradiol levels at time of discontinuation were 5.6 pg/mL (standard deviation 1.7). Estradiol levels increased after a 3-month treatment-free interval by a mean of 3.3 pg/mL (66%; P < .0001). Follicle-stimulating hormone and luteinizing hormone levels decreased from baseline by a mean of 7.5 mU/mL (P < .0001), and 1.4 mU/mL (P = .0062), respectively. Triglycerides decreased from baseline by a mean of 8.6 mg/dL (P = .036), and osteocalcin increased by a mean of 2.8 ng/mL (P = .013).

Conclusion: Intermittent letrozole significantly affects estradiol levels.