Exploratory Analysis of PTEN Deficiency by Immunohistochemistry from the Phase III CAPItello-291 Trial.

Randomized trialClinical cancer research : an official journal of the American Association for Cancer Research· Aug 2026

Exploratory Analysis of PTEN Deficiency by Immunohistochemistry from the Phase III CAPItello-291 Trial.

Komal Jhaveri, Hope S Rugo, Javier Cortés … Nicholas C Turner

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Breast & Gynecologic PathologyRandomized trialQ1IF 9.3

In PTEN-deficient tumors by immunohistochemistry, capivasertib plus fulvestrant nearly halved progression risk

Exploratory Analysis of PTEN Deficiency by Immunohistochemistry from the Phase III CAPItello-291 Trial.

Komal Jhaveri … Nicholas C Turner

Clinical cancer research · Aug 2026

Purpose

The phosphoinositide 3-kinase (PI3K)/AKT serine/threonine kinase (AKT) pathway is frequently activated in hormone receptor (HR)-positive/human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer, with loss of phosphatase and tensin homolog (PTEN) activity contributing to this activation.

Methods

This exploratory analysis was based on tumor samples collected from patients in the global phase III CAPItello-291 study.

n = 70

Results

PTEN-deficient tumors progressed about half as fast with capivasertib added

HR 0.52 (95% CI 0.28 to 0.90)

null 1

0.28

0.90

CI excludes the null - significant

More results

A total of 346 (94.3%) samples with a PTEN immunohistochemistry test result also had next-generation sequencing test results available for PIK3CA/AKT1/PTEN alteration status.

More results

When comparing PTEN deficiency by immunohistochemistry with PTEN alteration status by next-generation sequencing, the overall, positive, and negative percent agreements were 87.0% (301/346), 71.9% (23/32), and 88.5% (278/314), respectively.

“

Conclusion

These results suggest potential utility for immunohistochemistry in determining tumor PTEN status in breast cancer and raise the possibility of immunohistochemistry identifying additional patients who could benefit from treatment with capivasertib and fulvestrant.

Exploratory Analysis of PTEN Deficiency by Immunohistochemistry from the Phase III CAPItello-291 Trial.

Exploratory Analysis of PTEN Deficiency by Immunohistochemistry from the Phase III CAPItello-291 Trial.

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