Objective: This review describes historical development of selective estrogen receptor modulators (SERMs) and their combination with estrogens, termed a tissue selective estrogen complex (TSEC), and considers the potential for future TSEC development.
Methods: This narrative review is based on literature identified on PubMed and the TSEC research and development experience of the authors.
Results: SERMs have estrogenic and antiestrogenic effects in various tissues; however, no single agent has achieved an optimal balance of agonist and antagonist effects for the treatment of menopausal symptoms. Clinically, a number of SERMs protect against osteoporosis and breast cancer but can exacerbate vasomotor symptoms. Estrogens alleviate menopausal hot flushes and genitourinary symptoms as well as reduce bone loss, but the addition of a progestogen to menopausal hormone therapy to protect against endometrial cancer increases vaginal bleeding risk, breast tenderness, and potentially breast cancer. The search for an effective menopausal therapy with better tolerability led to the investigation of TSECs. Clinical development of a TSEC consisting of conjugated estrogens/bazedoxifene increased understanding of the importance of a careful consideration of the combination's components and their respective doses to balance safety and efficacy. Bazedoxifene is an estrogen receptor agonist in bone but an antagonist/degrader in the endometrium, which has contributed to its success as a TSEC component. Other oral TSEC combinations studied thus far have not demonstrated similar endometrial safety.
Conclusions: Choice of SERM, selection of doses, and clinical trial data evaluating safety and efficacy are key to ensuring safety and adequate therapeutic effect of TSECs for addressing menopausal symptoms.