An exploratory circulating tumor DNA (ctDNA) analysis from the phase 3 CALLA trial has revealed the potential of liquid biopsy as a powerful prognostic tool in locally advanced cervical cancer, demonstrating that undetectable ctDNA at treatment cycle 6 was associated with at least a 95% reduction in risk of disease progression or death.
The findings, presented at the 2025 American Society of Clinical Oncology (ASCO) Annual Meeting, showed that patients with undetectable ctDNA at the start of cycle 6 experienced dramatically improved outcomes regardless of whether they received durvalumab (Imfinzi) plus chemoradiotherapy (CRT) or CRT plus placebo.
Dramatic Risk Reduction with Undetectable ctDNA
The analysis demonstrated striking hazard ratios for patients with undetectable ctDNA at cycle 6, day 1. For progression-free survival (PFS), the risk reduction was consistent across both treatment arms: HR 0.04 (95% CI, 0.01-0.16) in the durvalumab arm and HR 0.04 (95% CI, 0.01-0.17) in the placebo arm. Overall survival (OS) showed similarly impressive results, with HR 0.04 (95% CI, 0.01-0.20) in the experimental arm and HR 0.04 (95% CI, 0.01-0.19) in the placebo arm.
"This preplanned exploratory ctDNA analysis of a large, global locally advanced cervical cancer population from CALLA demonstrates the high sensitivity of a personalized assay for ctDNA detection," said lead study author Jyothi Mayadev, MD, a professor of Radiation Medicine and Applied Sciences at the University of California, San Diego Health.
Baseline ctDNA Levels Predict Treatment Response
The analysis revealed that baseline ctDNA levels also served as important prognostic indicators. Patients with low ctDNA levels (below the median) at baseline demonstrated improved PFS compared with those having high ctDNA levels in both the durvalumab arm (HR, 0.60; 95% CI, 0.27-1.33) and placebo arm (HR, 0.62; 95% CI, 0.31-1.23).
OS outcomes similarly favored patients with low baseline ctDNA in the durvalumab arm (HR, 0.63; 95% CI, 0.27-1.45) and placebo arm (HR, 0.85; 95% CI, 0.43-1.69). Notably, the durvalumab regimen showed improved outcomes across both high and low baseline ctDNA populations.
High Sensitivity Detection and Treatment Monitoring
The study utilized the ultrasensitive, tumor-informed minimal residual disease (MRD) assay NeXT Personal for ctDNA detection. At baseline, ctDNA positivity rates were remarkably high at 99% in both treatment arms (92/93 patients in the CRT arm and 91/92 patients in the durvalumab/CRT arm).
By cycle 6, day 1, ctDNA positivity rates decreased substantially to 36% in the CRT arm (24/66 patients) versus 23% in the durvalumab/CRT arm (15/64 patients), demonstrating the treatment's effectiveness in clearing circulating tumor DNA.
PD-L1 Status Influences ctDNA Clearance
The analysis revealed differential ctDNA clearance patterns based on PD-L1 tumor area positivity (TAP) status. In patients with PD-L1 TAP of 20% or greater, the durvalumab/CRT combination showed superior ctDNA clearance compared to placebo/CRT, with ctDNA positivity rates of 19% versus 41% respectively at cycle 6, day 1—a 22% difference in detection rate.
Conversely, patients with PD-L1 TAP less than 20% showed minimal difference between treatment arms, with ctDNA positivity rates of 30% versus 32% in the durvalumab and placebo arms respectively, representing only a 2% difference.
Early Detection Provides Prognostic Advantage
ctDNA detection at cycle 3, day 1 emerged as a significant negative prognostic factor for both PFS and OS. Undetectable ctDNA at this early timepoint was associated with improved PFS in both the durvalumab arm (HR, 0.23; 95% CI, 0.11-0.50) and placebo arm (HR, 0.15; 95% CI, 0.07-0.33).
The clinical utility of early ctDNA monitoring was further demonstrated by progression patterns: 68% of patients with detectable ctDNA at cycle 3, day 1 experienced subsequent disease progression before data cutoff, while 83% of patients with undetectable ctDNA had not experienced disease progression by the same timepoint. The median lead time between cycle 3, day 1 ctDNA detection and disease progression was 164 days (range, 46-497 days).
Study Design and Patient Population
The CALLA trial was a randomized, double-blind, multicenter, placebo-controlled global study evaluating durvalumab plus CRT in female patients aged 18 years or older with locally advanced cervical cancer. Eligible patients had histologically confirmed cervical adenocarcinoma, squamous carcinoma, or adenosquamous carcinoma that was stage IB2 to IIB and node positive, or FIGO (2009) stage IIIA to IVA disease regardless of nodal status.
Patients were stratified by disease stage and global region, then randomly assigned 1:1 to receive either durvalumab/CRT or CRT alone. Plasma samples were collected and processed on cycle 1, day 1; cycle 3, day 1; and cycle 6, day 1. The primary endpoint was investigator-assessed PFS per RECIST 1.1 criteria, with OS as the secondary endpoint and ctDNA analysis as a key exploratory endpoint.
