Feasibility and interim results from the prospective international LS-URO study: Urine tumor DNA-based screening for urothelial cancer in Lynch syndrome carriers

Introduction : Lynch syndrome (LS) is a hereditary cancer syndrome caused by germline variants in DNA mismatch repair (MMR) genes ( MSH2 , MLH1 , MSH6 and PMS2 ), with up to 25% lifetime risk for urothelial cancer (UC). LS-UCs are commonly located in the upper urothelial tract, where tumors are difficult to detect early. No evidence-based screening strategy exists. We and others have shown that UC can be sensitively detected using urine tumor DNA (utDNA) mutation analysis. Methods : LS-URO is an international, prospective, multicenter study enrolling LS carriers aged 50-75 years from the Finnish LS Registry and the BC Cancer Hereditary Cancer Program. Participants receive an at-home 100-mL urine collection kit (with preservative) for mail return. Urine cell pellet DNA is analyzed using the UroScout 25-gene deep targeted sequencing assay, which includes common UC drivers (e.g., FGFR3 , ARID1A , KMT2D ) and MMR genes. Samples with ≥2 somatic mutations are reviewed by a molecular tumor board, with utDNA-positive cases examined by cystoscopy, urine cytology and imaging, as well as repeat urine sequencing. Results : Between May 2023 and October 2025, 213 participants were recruited, and 160 returned urine samples. Mean participant satisfaction with the urine collection procedure was 4.46/5. utDNA analysis is complete for 135 participants (76 Finland, 59 Canada). Nine (6.7%) participants were utDNA-positive with a median cancer fraction of 9% (range 4-17%) and median of four somatic mutations detected per sample (range 3-18). In 8/9 (89%) utDNA-positive participants, a somatic MMR second hit beyond the germline defect was detected. A total of 28 follow-up urine samples from five initially utDNA-positive participants revealed consistent detection of original mutations, with new mutations emerging in four. Eight out of nine (89%) positive participants harbored an FGFR3 hotspot mutation (of which 88% R248C ), whereas only one out of nine (11%) carried a TERT promoter mutation, consistent with our published observation that such mutations are rare in LS-UC. Two asymptomatic UC cases have been confirmed (one at initial examination, one 28 months after the first utDNA-positive screening sample during protocol-scheduled follow-up CT imaging). Four positive cases are pending initial urologic investigation, and the remainder are under continued surveillance through additional sampling and clinical follow-up. Conclusions: utDNA-based screening in LS is feasible, well accepted, and enables early, non-invasive cancer detection. Interim results demonstrate high compliance and promising diagnostic yield, pending long-term clinical follow-up. These findings support large-scale implementation of urine biopsy-based screening, to be further evaluated in the randomized PREDI-LYNCH trial.