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Preclinical data suggests tumors with PTEN loss develop a heightened dependence on the mTOR pathway. This provides a strong biological rationale for selecting an mTOR inhibitor, like getatolisib, over an AKT or PI3K inhibitor in this specific patient subpopulation for potentially better efficacy.
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Experts theorize that because resistance to PI3K inhibitors often involves downstream AKT activation, subsequent use of an AKT inhibitor is logical. However, re-challenging the pathway with a PI3K/mTOR agent like getatolisib after an AKT inhibitor has already failed is seen as less rational based on pathway biology.
Retrospective analysis of the BOLERO-2 trial revealed that the mTOR inhibitor everolimus benefits patients irrespective of their PI3K mutation status. This challenges the assumption that pathway-targeted therapies are only effective when a specific mutation is present, suggesting broader mechanisms of action.
The CAPItello-281 trial shows the benefit of the AKT inhibitor capivasertib is on a spectrum. Patients with 100% PTEN protein loss by IHC derive a much greater benefit than those with partial loss, suggesting a quantitative biomarker may optimize patient selection.
Data from older studies suggests that PI3K inhibitors and mTOR inhibitors (like everolimus) have distinct mechanisms and may not be cross-resistant. This allows clinicians to confidently sequence these agents, for example using everolimus after progression on a PI3K or AKT inhibitor, providing more lines of targeted therapy.
The IV drug gedatolisib, which inhibits the entire PI3K/AKT/mTOR pathway, is highly effective even in patients *without* PIK3CA mutations. This suggests pathway activation is not solely mutation-driven and creates a new option for a biomarker-negative patient group.
The VICTORIA-1 trial found that gedatolisib, a pan-PI3K/mTOR inhibitor, significantly improves progression-free survival in patients with PIK3CA *wild-type* tumors after CDK4/6 inhibitor progression. This is a crucial finding for a patient group lacking clear targeted options and broadens the utility of targeting the PI3K pathway beyond just mutated tumors.
Exploratory analysis shows that while patients with 100% PTEN loss have a much worse natural history than those with 90% loss, the therapeutic effect of capivasertib is stable across this spectrum. The drug effectively targets the pathway regardless of the magnitude of loss, making it a robust option for this entire subgroup.
The CAPItello-281 trial showed that the clinical benefit of adding the AKT inhibitor capivasertib is directly proportional to the degree of PTEN loss. The greatest separation in survival curves was seen in patients with 99-100% PTEN loss by IHC, suggesting the current trial entry cutoff of >90% may be too broad for optimal patient selection.
The VICTORIA-1 trial demonstrated remarkable efficacy for the getatolisib/palbociclib/fulvestrant triplet in patients *without* PIK3CA mutations. Its ability to nearly quadruple median PFS versus fulvestrant alone (9.3 vs 2.6 months) in this wild-type population addresses a major unmet need, as these patients previously lacked effective targeted therapies in the PI3K/mTOR pathway.
The CAPITELLO-281 trial found that while adding capivasertib to hormonal therapy was positive overall for PTEN-deficient prostate cancer, the benefit was most significant in patients with the most profound PTEN loss. This suggests that a simple positive/negative test may be insufficient, and quantitative IHC scoring could be necessary to select patients.