Early Phase 3 trials like JAVELIN adding immunotherapy to chemoradiation failed to improve outcomes. However, subgroup analyses consistently showed a potential benefit in PD-L1 high-expressing patients, a crucial lesson that informed the design of subsequent, more successful studies.

Cancers with estrogen receptor (ER) expression of 50% or less, while technically HR+, often behave biologically like basal or triple-negative tumors. These cancers are not primarily endocrine-driven and show a significant benefit from the addition of immune checkpoint inhibitors, challenging traditional subtype classifications.

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 CheckMate 9LA regimen provides exceptional benefit to PD-L1 negative and squamous histology NSCLC patients. This is significant because these subgroups often respond poorly to other immunotherapy combinations, with Dr. Carbone noting some trials where the control arm outperformed pembrolizumab in these patients.

In frontline clinical trials for KRAS G12C NSCLC, combining olomorasib with pembrolizumab alone yielded a 90% response rate in patients with >50% PD-L1 expression. This surpassed the 78% rate seen when chemotherapy was added, suggesting a more targeted approach may be superior for this specific biomarker-defined subgroup.

In the Keynote 522 trial for early-stage TNBC, adding pembrolizumab to chemotherapy resulted in only a modest improvement in pathological complete response (pCR). Surprisingly, this small initial gain translated into much more robust and significant long-term improvements in event-free and overall survival.

After numerous failed trials suggested immunotherapy was ineffective in ovarian cancer, the KEYNOTE B96 study marks a turning point. Combining pembrolizumab with chemotherapy showed statistically significant improvements in both progression-free and overall survival in platinum-resistant patients, reviving the entire therapeutic class for this disease.

Genomic risk factors like TP53 mutations can predict immunotherapy failure mechanisms. In a case of TP53-mutated ALL, treatment with blinatumomab led to relapse with CD19-dim or negative disease. This suggests the underlying genomics predispose the cancer to shed its target antigen under therapeutic pressure.