The O22 trial's positive result for adjuvant Pembrolizumab plus Belzutafan was unexpected, as experts believed kidney cancer recurrence was primarily immune-driven, not HIF-driven. This outcome forces a re-evaluation of the underlying biology of recurrence and suggests a significant role for HIF inhibition in the adjuvant setting.

Despite initial preclinical concerns that HIF-2 inhibition might dampen immune response, the success of the Pembro+Belzutifan combination is likely due to the simple additive effect of two active drugs. Newer data refutes the immune-dampening theory, showing no negative impact on the tumor microenvironment and possibly even a reduction in immunosuppressive cells.

An FDA analysis showed the survival curve for kidney cancer patients on IO-IO therapy (ipinevo) is much flatter for those with early tumor growth compared to IO-TKI regimens. This suggests early progression on a dual-mechanism IO-TKI therapy indicates true resistance, while on IO-IO it could be delayed response.

Developers often test novel agents in late-line settings because the control arm is weaker, increasing the statistical chance of success. However, this strategy may doom effective immunotherapies by testing them in biologically hostile, resistant tumors, masking their true potential.

The PEACE-3 steering committee felt its initial positive OS signal was unreliable due to non-proportional curves, despite meeting the statistical goal. This suggests a high level of self-imposed rigor, as early curve crossing can be due to statistical chance when event numbers are low, rather than a true lack of benefit.

Despite Belzutafan's clinical successes, effective biomarkers for patient selection are almost non-existent. Experts anticipate a significant increase in understanding over the next 12-24 months from correlative studies, which will likely reveal novel gene expression and tissue-based markers beyond obvious candidates like serum EPO.

Previous adjuvant trials in kidney cancer using more toxic VEGF-TKIs largely failed. Belzutifan's success suggests that in the adjuvant setting, a drug's tolerability and the ability for patients to maintain dose intensity are more critical for efficacy than raw potency in advanced disease. TKIs were often too toxic for patients to endure for a full year.

A sophisticated concern regarding the HIF-2 inhibitor belzutifan is its potential to diminish kidney cancer's antigenicity by reducing human endogenous retrovirus expression. While providing an early benefit, this could theoretically make tumors less responsive to subsequent immunotherapies, negatively impacting long-term outcomes—a critical consideration for sequencing.

The study presented three different datasets over a short period. While efficacy endpoints like PFS and OS changed, the toxicity data remained identical. This is highly unusual, as resolving censored patient data for efficacy should also lead to updated toxicity information, suggesting a rushed or incomplete analysis process.