Selective estrogen receptor modulators in clinical practice: a safety overview

Introduction: Selective estrogen receptor (ER) modulators (SERMs) are a class of nonsteroidal compounds that interact with ERs, each with a distinct tissue-specific profile. Depending upon the degree of ER agonism/antagonism at the target tissue, SERMs show efficacy for various indications including osteoporosis, dyspareunia, and breast cancer, and are associated with safety risks. Areas covered: This review describes the safety profile of SERMs (tamoxifen, raloxifene, toremifene, bazedoxifene, lasofoxifene, and ospemifene) and fulvestrant (a pure ER antagonist) from Phase III trials, long-term extension studies, and active comparator studies. Tamoxifen, a first-generation SERM, is indicated for breast cancer prevention and treatment but is associated with serious safety concerns including endometrial cancer, venous thromboembolic events (VTE), and stroke. Toremifene, raloxifene, bazedoxifene, lasofoxifene, and ospemifene present generally improved, though distinctly different, safety profiles compared with tamoxifen, especially with endometrial cancer and stroke. However, the risk of VTE remains a concern for most SERMs. Expert opinion: Each SERM presents a unique risk/benefit profile based on varying indications and tissue-specific ER agonist and antagonist effects, making careful patient selection and ongoing patient monitoring crucial aspects of treatment. Future research may focus on identifying new SERMs for endocrine-resistant and endocrine-responsive cancers and post-menopausal symptoms.