Open Access

Objectives Liquid biopsy (LBx) provides diagnostic, prognostic and predictive insights for malignant diseases and offers promising applications regarding tumor burden, tumor heterogeneity and clonal evolution. Methods ALPS is a prospective trial for patients with metastatic cancer that comprises sequential collection of LBx samples, tumor tissue, radiological imaging data, clinical information and patient-reported outcomes. Peripheral blood plasma is collected based on the individual patient’s staging intervals and LBx-derived ctDNA analyses are performed using CAncer Personalized Profiling sequencing (CAPP-seq). Results From April 2021 to October 2023, 419 patients have been enrolled. A total of 1,293 LBx samples were collected, 419 samples (100 %) at the beginning of the study and an average of 3 (range 1–12) during the 30-month follow-up period of the current interim analysis. 380 tissue biopsy (TBx) samples (90.7 %) were available at baseline and 39.6 % had ≥1 TBx samples at follow-up. Lung cancer patients are most prevalent in ALPS (n=147), followed by colorectal (n=38), prostate (n=31) and gastroesophageal cancer (n=28). On average, 12.0 ng/mL plasma cell-free DNA (cfDNA) could be isolated. First CAPP-seq analyses in 60 patients comprised 110 samples and demonstrated a detection sensitivity of 0.1 %. Conclusions The first interim analysis of ALPS confirms feasibility for comprehensive longitudinal evaluation of LBx and demonstrates suitability for ctDNA evaluation.