Experts advocate for using AKT inhibitors in the early, hormone-sensitive setting for PTEN-deficient prostate cancer. The rationale is that early-stage disease is more dependent on the AKT pathway. In later, castrate-resistant stages, the cancer develops other resistance mechanisms and alterations, diminishing the potential impact of a targeted AKT inhibitor.

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.

The AKT pathway, activated by PTEN loss, drives cancer growth independently of the androgen receptor, which controls PSA production. This discordance means clinicians cannot rely on PSA alone and must use systematic imaging to detect progression in this specific patient subgroup.

Using capivasertib in the hormone-sensitive setting is preferred because the cancer is more likely dependent on the AKT pathway for growth. In later, castration-resistant stages, additional genetic alterations can emerge, creating redundant growth signals and potentially diminishing the inhibitor's efficacy.

The panel suggests AKT inhibitor trials in prostate cancer have been disappointing due to suboptimal biomarker selection (e.g., PTEN IHC). A similar drug in breast cancer showed significant survival benefit when using a more precise NGS-based strategy, indicating a potential path forward if the right patient population is identified genetically.

In patients with PTEN loss, cancer growth is driven by the PI3K-AKT pathway, which doesn't activate the PSA gene. This can lead to significant disease progression with a low or stable PSA, making PSA a poor surrogate for disease activity in this sub-population.

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 ongoing Alliance ASPIRE trial is one of the first to use tumor biology, specifically alterations in suppressor genes like P10, P53, and RB1, as a primary stratification factor. This marks a significant move away from relying on imaging-based volume criteria (high vs. low) to determine prognosis and predict who may benefit from chemotherapy.