SERDs in ER-Positive Breast Cancer: Current Role and Evidence

Introduction to SERDs

The National Comprehensive Cancer Network recommends Selective Estrogen Receptor Degraders (SERDs) as established, guideline-recommended agents for ER-positive metastatic breast cancer, with fulvestrant being the standard SERD since 2009 and newer oral SERDs like elacestrant approved in 2023 for ESR1-mutated disease 1, 2, 3

Fulvestrant 500 mg IM monthly is a Category 1 preferred option for postmenopausal women with HR-positive, HER2-negative metastatic breast cancer, either as monotherapy or combined with CDK4/6 inhibitors, as recommended by the National Comprehensive Cancer Network 4, 5
Fulvestrant plus CDK4/6 inhibitor (palbociclib, ribociclib, or abemaciclib) is the preferred first-line approach based on overall survival benefits demonstrated in multiple phase III trials, according to the National Comprehensive Cancer Network 4, 5
Fulvestrant combined with a CDK4/6 inhibitor should be offered to patients with progressive disease during AI treatment or who recur within 12 months of adjuvant AI therapy (Category 1 recommendation), as stated by the American Society of Clinical Oncology 5

For postmenopausal women with HR+/HER2- metastatic disease, the preferred first-line treatment is CDK4/6 inhibitor + AI OR CDK4/6 inhibitor + fulvestrant, as recommended by the National Comprehensive Cancer Network 4, 5
For premenopausal women, all SERD-containing regimens require concurrent ovarian suppression with LHRH agonist (goserelin or leuprolide), according to the American Society of Clinical Oncology 5, 6

Fulvestrant should be administered at 500 mg IM monthly (with loading dose of 500 mg on days 1, 15, and 29 of first month), as recommended by the National Comprehensive Cancer Network 4
When combining fulvestrant with CDK4/6 inhibitors, monitor CBC every 2 weeks for first 2 cycles, then at start of each cycle, as suggested by the European Society for Medical Oncology 7

Do not continue the same CDK4/6 inhibitor after progression—limited data support switching to another CDK4/6-containing regimen, as stated by the National Comprehensive Cancer Network 4
Do not use fulvestrant at the old 250 mg dose—500 mg monthly is superior and the only recommended dose, according to the American Society of Clinical Oncology 9
Do not forget ovarian suppression in premenopausal women receiving fulvestrant—incomplete suppression leads to treatment failure, as recommended by the European Society for Medical Oncology 6