The Lidara study showed SERD benefit in patients without pre-existing ESR1 mutations. Success is likely multifactorial: SERDs are more effective and better tolerated than AIs. Critically, they also prevent the most common resistance mechanism—the acquisition of ESR1 mutations—from developing in the first place, altering the disease's future trajectory.

The development of SERDs for adjuvant therapy was stalled for two decades not by efficacy concerns, but by logistics. Fulvestrant, the first SERD, required monthly intramuscular injections, a pragmatically unfeasible strategy for a 5-year adjuvant trial, a problem only solved with the advent of oral SERDs.

Transdermal estradiol is gaining renewed attention as an ADT option. Recent trials show it is non-inferior to standard LHRH analogs, offering a different side effect profile. This allows clinicians to trade side effects like hot flashes for gynecomastia, enabling more personalized treatment decisions.

Selective Estrogen Receptor Degraders (SERDs) are a mechanistic advance over older therapies. While drugs like tamoxifen merely block estrogen receptors and AIs reduce estrogen, SERDs both block the receptor and trigger its complete degradation, removing the target altogether.

With multiple FDA-approved oral SERDs available, clinical decision-making is heavily influenced by their distinct side effect profiles. Elacestrant predominantly causes nausea, while iminoralestrant causes diarrhea. This distinction is a primary factor in tailoring treatment to individual patients.

Uniquely, the EMPRIS window study in premenopausal patients showed geridestran monotherapy was more effective at suppressing proliferation than tamoxifen without adding an LHRH agonist. This challenges the standard practice of mandatory ovarian function suppression and could simplify treatment for younger women.

An ESR1 mutation locks the estrogen receptor in a permanently "on" state, independent of estrogen. This renders aromatase inhibitors (AIs) ineffective but means therapies that degrade the receptor itself, like SERDs, can still be effective treatment options.

A significant, immediate use for adjuvant oral SERDs like gerodestrant will be for patients who cannot tolerate the arthralgias and other side effects of standard aromatase inhibitors (AIs). This addresses a large and challenging clinical problem, positioning SERDs as a key alternative for maintaining long-term adherence to endocrine therapy.

Unlike some endocrine therapies, oral SERDs used in premenopausal women require concurrent ovarian suppression (e.g., with a GnRH agonist). This is a critical safety measure to mitigate the risk of developing ovarian cysts, a potential side effect of using these agents without adequately suppressing ovarian function.