Tamoxifen-related endocrine symptoms in Chinese patients with breast cancer: Study protocol clinical trial (SPIRIT Compliant)

BACKGROUND: Breast cancer is the most prevalent cancer in females and disease recurrence remains a significant problem. To prevent recurrence, tamoxifen is prescribed for at least 5 years. However, among patients who receive tamoxifen, individual responses are highly variable. These responses are affected by the type, frequency, and severity of endocrine symptoms, as well as adherence rates. Polymorphisms in genes involved in the metabolism of tamoxifen (ie, CYP3A4, CYP2D6) may influence responses to tamoxifen. In this study, the inter-relationships among endocrine symptoms, drug adherence, and genetic polymorphisms in Chinese breast cancer patients receiving tamoxifen therapy will be examined. We hypothesize that patients with more severe endocrine symptoms will be less likely to adhere to tamoxifen treatment. In addition, we hypothesize that a relationship will exist between the severity of tamoxifen-induced symptoms and allelic variations in tamoxifen metabolism-related genes. Although many association studies have determined that select genotypes influence the efficacy of tamoxifen, very few studies have investigated for associations between tamoxifen-induced endocrine symptoms and these polymorphisms. OBJECTIVES: The aim of this study was to characterize genetic polymorphisms in tamoxifen metabolism-associated genes in Chinese women with breast cancer and to explore the inter-relationships between genetic polymorphisms, endocrine symptoms, and adherence to tamoxifen. METHOD: We will conduct a prospective cohort study that follows 200 Chinese women over 18 months and assess treatment-related symptoms and genetic variations. Endocrine symptoms and drug adherence will be determined through interview-administered standardized questionnaires. Polymorphisms in drug metabolism genes will be determined using real-time polymerase chain reaction based genotyping method. Data will be analyzed to determine associations between allelic variations, endocrine symptoms, and adherence. DISCUSSION: The proposed study will evaluate for polymorphisms in gene(s) that are associated with tamoxifen-related endocrine symptoms and adherence with tamoxifen. We will explore the relationships between genotypes, endocrine symptoms, and drug adherence in Chinese breast cancer patients. Findings from this study may assist clinicians to identify patients at higher risk for a worse symptom experience and lower adherence rates and enable them to initiate appropriate interventions. In the long term, the findings from this study may be used to develop and test tailored symptom management interventions for these patients.