Conditional survival data from the RUBY trial is highly encouraging. For MSI-high patients, reaching the one-year survival mark implies an 84% chance of long-term survival, which skyrockets to nearly 95% for those who reach the three-year landmark.

Following the Keynote B21 trial, clinicians have become more selective with adjuvant immunotherapy in endometrial cancer. The study showed minimal benefit for pMMR patients and less impressive gains overall in its lower-risk population compared to advanced disease trials. This has led to a practice of reserving adjuvant chemo-IO primarily for stage 3 dMMR patients.

The GOG-B21 trial found that while adding pembrolizumab to chemotherapy benefits the dMMR subgroup, it paradoxically leads to worse outcomes in the pMMR subgroup. This highlights the critical need for molecular testing to avoid potential harm.

Based on translational data from the RUBY trial, experts are most cautious about recommending frontline checkpoint inhibitors for patients in the "No Specific Molecular Profile" (NSMP) subgroup of pMMR endometrial cancer, suggesting this group may not benefit.

The KEYNOTE-B21 adjuvant trial revealed a crucial paradox: adding pembrolizumab may worsen outcomes for mismatch repair proficient (pMMR) patients (HR 1.2), while being highly beneficial for dMMR patients. This highlights that metastatic and adjuvant settings are not equivalent.

Data from DUO-E and RUBY Part 2 trials show adding a PARP inhibitor to chemo-immunotherapy provides only a small PFS benefit. Experts are not convinced of its value, citing a lack of overall survival benefit and potential for harm.

While immunotherapy is transformational for DMMR endometrial cancer, its benefit is much smaller for the PMMR majority (two-thirds of patients). This reality requires more nuanced patient counseling and selective use in this population.

The RUBY trial surprisingly revealed that patients with p53-mutated tumors, a subset of the generally less responsive pMMR group, derive significant benefit from adding immunotherapy to chemotherapy, challenging previous assumptions about this molecular subtype.

The rationale for adding PARP inhibitors to immunotherapy in endometrial cancer is to induce DNA damage and cell death. This process creates neoantigens, potentially making tumors more recognizable and vulnerable to the immune system, especially in PMMR patients.