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.

The four TCGA molecular profiles (e.g., POLE-mutated, p53-abnormal) have evolved beyond predicting outcomes to actively guiding treatment, such as de-escalating therapy for low-risk groups and escalating for high-risk ones.

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.

As various maintenance therapies (immunotherapy, ADCs) are integrated into endometrial cancer treatment, the next major clinical question is defining how long these agents need to be continued to maximize benefit while minimizing long-term toxicity and patient burden.

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 former high-risk group (Stage 3b) was traditionally excluded from major clinical trials. The new staging system demonstrates that these patients have better-than-expected outcomes with modern therapy and should be included in future studies. It simultaneously identifies a new ultra-high-risk group (Stage 3c) that requires entirely different trial designs.

Inconsistent methods for assessing biomarkers like PD-L1 (CPS vs. TAP scoring), p53 (IHC vs. sequencing), and HRR (different panels) across major clinical trials make it difficult to compare results and identify a reliable predictive marker for endometrial cancer.

While circulating tumor DNA (ctDNA) is currently hard to act on for escalating treatment, its most promising near-term application may be in identifying patients who can safely stop or reduce therapy, rather than determining when to start it.