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The approval of the AKT inhibitor Capivasertib has transformed PTEN testing from a prognostic tool for aggressive disease into a mandatory predictive test. Every patient with newly diagnosed metastatic prostate cancer should be assessed to determine eligibility for this targeted therapy, marking a significant shift in the standard of care.
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The efficacy of the AKT inhibitor Capivasertib is not uniform across all PTEN-deficient tumors. An analysis revealed that patients with 100% loss of the PTEN protein experienced the most significant benefit, with a 12-month improvement in radiographic progression-free survival. This highlights a direct correlation between the degree of protein loss and treatment response.
The prevalence of PTEN loss is not static; it increases significantly as prostate cancer advances. While less common in localized disease, it can be found in up to 25% of patients with metastatic disease. This escalating frequency with disease progression underscores its role as a key driver of cancer advancement and a critical therapeutic target in later stages.
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.
Because PTEN loss is an early, truncal mutation in prostate cancer, clinicians should perform NGS testing on the first day a patient is seen. This proactive approach ensures that crucial biomarker information is not lost and is available to guide future treatment decisions, such as the use of an AKT inhibitor, should the disease progress.
While Next-Generation Sequencing (NGS) is common, the FDA label for Capivasertib specifically requires Immunohistochemistry (IHC) to establish PTEN deficiency for treatment eligibility. This is because the critical factor is the functional loss of the PTEN protein, which IHC directly measures, making it non-negotiable for insurance approval.
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.
Unlike androgen receptor mutations which arise under treatment pressure, PTEN loss is an earlier event. Therefore, archival tissue from a primary biopsy is generally sufficient for determining PTEN status, even years later at metastatic relapse, avoiding a new invasive procedure.
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.
Unlike androgen receptor mutations that arise under treatment pressure, PTEN loss is an earlier event. Therefore, tissue from an original biopsy or prostatectomy remains informative for testing PTEN status when a patient relapses with metastatic disease, simplifying the diagnostic process and avoiding invasive re-biopsies.
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.