ctDNA: A Minimally Invasive Option for HR+ Breast Cancer Biomarker Testing

Data analyzed from the phase 3 CAPItello-291 trial (NCT04305496), which evaluated capivasertib (Truqap) combined with fulvestrant (Faslodex) in individuals with hormone receptor–positive breast cancer, indicated that circulating tumor DNA (ctDNA) offers a minimally invasive alternative for identifying PIK3CA, AKT1, and PTEN alterations in these patients when adequate tissue for testing is not accessible.¹

Findings presented at the 2025 San Antonio Breast Cancer Symposium demonstrated that within the overall study population (n = 708), 658 patients had sample available for ctDNA analysis. Within that subgroup, PIK3CA/AKT1/PTEN alterations were detected via ctDNA in 279 patients, whereas 379 patients did not have these alterations detected. Within the ctDNA-detected group, 149 patients also had co-occurring ESR1 mutations.

When comparing tissue vs ctDNA testing, 207 patients were positive for PIK3CA/AKT1/PTEN alterations in both ctDNA and tissue; 30 were positive in ctDNA and negative in tissue; 42 were positive in ctDNA with unknown tissue status; 63 were positive via tissue and negative with ctDNA; and 17 were positive in tissue with unknown ctDNA status. This translated to an overall percentage agreement (OPA) of 83.3% and a percentage positive agreement (PPA) of 76.7%.

For PIK3CA alterations specifically, the OPA and PPA were 88.9% and 77.1%, respectively. These respective rates were 98.7% and 83.8% when looking at AKT1 alterations. The OPA and PPA were 90.9% and 54.2%, respectively, in regard to PTEN alterations.

“If we look at association of tumor fraction, we can improve the ability to identify patients with low ctDNA shedding, where ctDNA testing alone may miss alterations,” lead study author Nicholas Turner, MD, PhD, FRCP, FMedSci, said in a presentation of the data.

Turner is head of the Ralph Lauren Centre for Breast Cancer Research Breast Unit, director of Clinical Research, and director of The Royal Marsden and Institute of Cancer Research NIHR Biomedical Research Centre in London, United Kingdom.

Previous Data From CAPItello-291

Findings published in the New England Journal of Medicine showed that in the overall trial population, those treated with capivasertib plus fulvestrant (n = 355) achieved a median progression-free survival (PFS) of 7.2 months (95% CI, 5.5-7.4) compared with 3.6 months (95% CI, 2.8-3.7) for those given placebo plus fulvestrant (n = 353; HR, 0.60; 95% CI, 0.51-0.71; P < .001).² For patients harboring AKT pathway alterations, the median PFS was 7.3 months (95% CI, 5.5-9.0) with capivasertib plus fulvestrant (n = 155) vs 3.1 months (95% CI, 2.0-3.7) for placebo plus fulvestrant (n = 134; HR, 0.50; 95% CI, 0.38-0.65; P < .001).

Based on these prior data, in November 2023, the FDA approved capivasertib plus fulvestrant for the treatment of adult patients with hormone receptor–positive, HER2-negative, locally advanced or metastatic breast cancer harboring 1 or more PIK3CA, AKT1, or PTEN alterations, as detected by an FDA-approved test, following progression on at least 1 endocrine-based regimen in the metastatic setting or recurrence on or within 12 months of completing adjuvant therapy.³

CAPItello-291 Trial Design

The randomized, double-blind, placebo-controlled trial enrolled patients at least 18 years of age with hormone receptor–positive, HER2-negative, locally advanced or metastatic breast cancer who experienced disease progression following prior treatment with an aromatase inhibitor, with or without a CDK4/6 inhibitor.² Up to 2 previous lines of endocrine therapy and 1 prior line of chemotherapy in the advanced setting were permitted.

Patients were randomly assigned 1:1 to receive capivasertib 400 mg twice per day for 4 days on and 3 days off plus fulvestrant at 500 mg once every 14 days; or placebo plus fulvestrant in 28-day cycles.

Investigator-assessed PFS in the overall population and patients with AKT pathway alterations served as the trial’s primary end point. Secondary end points included overall survival, objective response rate, and safety.

Efficacy Findings

The PFS benefit observed with the capivasertib regimen was consistent across ctDNA/tissue subgroups.¹ This included those with PIK3CA/AKT1/PTEN alterations detected by tissue only (HR, 0.50; 95% CI, 0.38-0.65), all patients with evaluable ctDNA (HR, 0.59; 95% CI, 0.50-0.71), those with PIK3CA/AKT1/PTEN alterations detected via ctDNA (HR, 0.43; 95% CI, 0.33-0.56), patients with ESR1 co-mutations detected via ctDNA (HR, 0.52; 95% CI, 0.36-0.76), patients without ESR1 co-mutations (HR, 0.36; 95% CI, 0.23-0.54), patients without PIK3CA/AKT1/PTEN alterations detected in ctDNA (HR, 0.76; 95% CI, 0.60-0.95), patients with PIK3CA/AKT1/PTEN alterations detected in ctDNA or tissue (HR, 0.49; 95% CI, 0.38-0.62), and those without PIK3CA/AKT1/PTEN alterations detected in either tissue or ctDNA (HR, 0.74; 95% CI, 0.58-0.95).

REFERENCES

1. Turner NC, Oliveira M, Howell SJ, et al. Capivasertib plus fulvestrant in hormone receptor-positive PIKЗСА/AKT1/PTEN-altered advanced breast cancer: exploratory cDNA analyses from the phase 3 CAPltello-291 trial. Presented at: 2025 San Antonio Breast Cancer Symposium; December 9-12, 2025; San Antonio, TX. Abstract RF7-05.

2. Turner NC, Oliveira M, Howell SJ, et al. Capivasertib in hormone receptor-positive advanced breast cancer. N Engl J Med. 2023;388(22):2058-2070. doi:10.1056/NEJMoa2214131

3. FDA approves capivasertib with fulvestrant for breast cancer. FDA. November 16, 2023. Accessed December 11, 2025. https://tinyurl.com/4ajuu8tt