A key heuristic for deciding between second-line endocrine therapy versus chemotherapy/ADC is the duration of benefit from the first-line CDK4/6 inhibitor. Patients who progress after a long duration (e.g., >18 months) are likely still endocrine-sensitive and should receive further endocrine-based therapy. Rapid progression (e.g., <6 months) suggests endocrine resistance, warranting a potential switch in modality.

The LIDERA trial's success is complicated because it was designed against a standard of care that is now outdated. It excluded CDK4/6 inhibitors, which are now common for high-risk patients, creating a gap in understanding how to integrate this new drug into modern clinical practice.

Patients who recur shortly after adjuvant CDK inhibitor therapy have aggressive tumors and a poor prognosis. Clinical series show that when these patients are treated with a CDK inhibitor in the first-line metastatic setting, the median progression-free survival is only around three months, indicating profound pre-existing resistance.

As effective antibody-drug conjugates (ADCs) move into earlier treatment lines for ovarian cancer, a new clinical challenge arises: treating patients who progress after receiving them. The field is just beginning to develop these 'post-ADC' therapies, highlighting a critical and urgent need for innovation in areas like DNA repair mechanism inhibitors (e.g., V1, CDK2) for this emerging patient population.

Patients are often exhausted after primary treatment and surprised by the recommendation for two additional years of intensive oral therapy. Clinicians should introduce this possibility early in the treatment journey to manage expectations and prevent the patient from feeling overwhelmed later on.

The LDERA trial showed early, significant benefit for adjuvant gerodestrant, an oral SERD. This positive result creates a clinical challenge: how to position this new agent relative to adjuvant abemaciclib, which has a proven overall survival benefit in high-risk patients but was not studied in combination with a SERD.

New CDK inhibitors that also target CDK2 show great activity in models resistant to current CDK4/6 agents. Instead of being reserved for later use, they are already being tested in frontline trials. The strategy, similar to that of ALK inhibitors in lung cancer, is that using the best drug first may prevent or significantly delay the onset of resistance.

Data from multiple trials (EMERALD, VERITEC-2) reveal that the duration of a patient's response to a prior CDK4/6 inhibitor acts as a key predictive biomarker. Patients who benefited from CDK4/6 inhibitors for longer periods (e.g., >12-18 months) subsequently experienced a significantly greater progression-free survival benefit from oral SERD therapy.

A simple clinical biomarker—having received a prior CDK4/6 inhibitor for over 12 months—identifies patients likely to achieve significant progression-free survival (nearly nine months) with single-agent elacestrant. This allows clinicians to select patients for monotherapy without complex genomic profiling.