Background: Cancer is a major public health and economic issue and is the leading cause of death worldwide. Up to 80% of cancer patients in Vietnam were diagnosed at stage III or stage IV, leading to a a low 5-year survival rate compared to other countries. Early cancer screening assays capable of identifying early-stage cancer patients among high-risk or asymptomatic individuals are essential to achieve better treatment outcomes and reduced mortality. We previously developed a multimodal LB-based assay named Screening for the Presence Of Tumor by Methylation And Size (SPOT-MAS) to detect the five most common cancer types in Vietnam (liver, breast, colorectal, gastric, and lung cancer). To be successfully applied as a population-wide screening test, the clinical performance of SPOT-MAS needs to be validated in a prospective study. Methods: Herein, we launched a prospective cohort study named K-DETEK (ClinicalTrials.gov identifier: NCT05227261) at 13 major hospitals and one research institute in Vietnam to assess the feasibility and performance of SPOT-MAS in a multi-center clinical trial setting. Our study recruited 10,000 asymptomatic participants participants aged 40 years or older and followed-up for 6 and 12 months. The performance was assessed by computing the number of cases with the detection of a signal (n, %), including a positive predictive value (PPV) and accuracy in detecting tumor tissue-of-origin (TOO). Results: At the time of abstract submission, our analysis of 2795 participants demonstrated its ability to detect cancers in asymptomatic individuals with a positive predictive value of 60%, with 83.3% accuracy in detecting tumor location. Furthermore, we presented a case report to support further using SPOT-MAS as a complementary method to achieve early cancer detection and provide the opportunity for early treatment. Conclusions: Our study has demonstrated the clinical application of a multi-cancer blood test in a low- and middle-income country like Vietnam, where a nationwide cancer screening program is urgently needed but currently not available. Beyond detecting cancer signals, our test predicted the tumor location, allowing clinicians to fast-track the follow-up diagnostic and guide any necessary treatment. Keywords: liquid biopsy, ctDNA, clinical validation, prospective trial, cancer screening. Clinical trial information: NCT05227261.