Abstract
Abstract Background: Low-dose estrogen might induce apoptosis in breast cancer cells that develop resistance to antihormonal therapy. Letrozole withdrawal for 3-month might permit estrogenic stimulation in residual resistant 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 ER and/or PgR ≥ 10% of the cells, node-negative early breast cancer were eligible. Patients (pts) received letrozole (2.5 mg daily) for five years with a 3-month treatment free interval after the 1st year of therapy. The primary endpoint was to evaluate the increase in serum estradiol absolute levels after 3-month treatment free interval. The secondary endpoints were the evaluation of others biological markers (e.g. FSH, LH, Cholesterol, HDL, triglycerides, osteocalcin). Estradiol levels were quantified by ECLIA assay that measured estradiol concentrations with a 5 pg/ml lower detection limit. FSH and LH levels (mU/ml) were measured by ECLIA assay, Osteocalcin (ng/ml) by RIA assay, Cholesterol, HDL, and Triglycerides (mg/ml) by colorimetric assay. Results: From November 2007 to February 2012, 130 evaluable pts were enrolled. The median age was 61 years. One-hundred ten pts (85%) had pT1 tumor, 88 pts (68%) presented grade 2 and 83 pts (64%) showed a Ki-67 LI <20%. 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 free interval by a mean of 3.3 pg/ml (66%; P <0.0001). FSH and LH levels decreased from baseline by a mean of 7.5 mU/ml (P<0.0001), and 1.4 mU/ml (P = 0.0062) respectively. Triglycerides decreased from baseline by a mean of 8.6 mg/dl (P = 0.036), and osteocalcin increased by a mean of 2.8 ng/ml (P = 0.013). Conclusions: Intermittent Letrozole significantly impact on estradiol levels. This study provides further evidence supporting the role of intermittent letrozole in the adjuvant treatment of postmenopausal patients with endocrine responsive breast cancer. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-13-12.
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