Efficacy of Tamoxifen Versus Toremifene in CYP2D6 IM/PM of Premenopausal Patients With ER-positive Early Breast Cancer

STUDY BACKGROUND Breast cancer is a serious disease that threatens human health and life. Especially in China, the incidence rate is increasing year by year. According to WHO data, the incidence of breast cancer in China in 2020 will reach 214,000. Selective estrogen receptor modulators (SERMs) are a classic form of endocrine therapy for early breast cancers, but not all hormone receptor positive breast cancers benefit from specific SERMs. Numerous studies have shown that CYP2D6 variant carriers (around 50% CYP2D6 variant carriers in Chinese population) will not benefit a lot from tamoxifen, and combined use of CYP2D6 inhibitors will further affect the efficacy of tamoxifen. However, studies on another SERM drug - toremifene have shown that its metabolism and pharmacological effects are not influenced by CYP2D6 genotype or enzyme activity. Therefore, in the principle of individualized medicine, it is necessary to compare the efficacy of using tamoxifen and toremifene in CYP2D6 variant carriers in China so as to provide more guidance for clinical use. OBJECTIVES: 1. The main purpose of this study is to compare 5-year disease-free survival rate of adjuvant endocrine therapy with tamoxifen and toremifene in premenopausal women with estrogen receptor-positive early breast cancer who are CYP2D6 intermediate/poor metabolizers. 2. The secondary purpose of this study includes: 1. To compare 5-year overall survival (OS) and safety of adjuvant endocrine therapy with tamoxifen and toremifene in premenopausal patients with estrogen receptor-positive early breast cancer who are CYP2D6 intermediate/poor metabolizers. 2. To compare the changes of plasma concentration of the parent drugs and metabolites of tamoxifen and toremifene in premenopausal patients with estrogen receptor-positive early breast cancer who are CYP2D6 intermediate/poor metabolizers. 3. To assess the pharmacokinetics of tamoxifen and toremifene in premenopausal patients with estrogen receptor-positive early breast cancer who are CYP2D6 intermediate/poor metabolizers. OUTLINE: First, CYP2D6 genotype screening shall be conducted in premenopausal patients with estrogen receptor-positive early breast cancer in order to determine the frequency of different alleles. Then, patients who are CYP2D6 intermediate/poor metabolizers (with \*4, \*5, \*10, \*14, \*17, \*41 alleles) shall be stratified and randomized at the ratio of 1:1 ratio: allele status of CYP2D6 CYP2D6 intermediate/poor metabolizer (Heterozygous or homozygous), lymph node metastasis (with vs. without), prior chemotherapy (with vs. without), and HER2 status (positive vs. negative). Included patients shall be divided into two groups. One group will be given Tamoxifen (10mg Bid) for 5 years and the other group will be given toremifene (60mg qd) for 5 years. Then 5-year disease-free rate and overall survival and safety will be compared between these two groups. At Month 6, pharmacokinetic study on tamoxifen, toremifene and their metabolites will be conducted on patients.