The Diagnostic Performance of a Four-Gene Digital Droplet PCR Panel for Urine Liquid Biopsy in Urothelial Bladder Cancer

<b>Background</b>: Urothelial bladder carcinoma (UBC) is a disease that lacks robust non-invasive laboratory biomarkers. Recently, urine liquid biopsy has emerged as a promising tool for diagnosis and surveillance of patients with these tumors. The aim of this study was to evaluate the diagnostic potential of a urinary tumor DNA detection panel, which included eight common point mutations in <i>TERT</i>, <i>GPR126</i>, <i>FGFR3</i>, and <i>PIK3CA</i> genes, in UBC. <b>Methods</b>: The study included patients with histologically confirmed UBC (<i>n</i> = 88) and patients with cystitis, bladder leiomyomas, or other non-malignant conditions (control group; <i>n</i> = 72). DNA was extracted from whole urine specimens. ddPCR analysis was performed using the Bio-Rad QX200 AutoDG ddPCR system. <b>Results</b>: Urinary tumor DNA detection panel demonstrated a sensitivity of 78.4% and a specificity of 100% (AUC-ROC = 0.892). Detection rates for the analyzed mutations were the following: 54.5%, 37.5%, 28.4%, and 38.6% for <i>TERT</i>, <i>GPR126</i>, <i>FGFR3</i>, and <i>PIK3CA</i>, respectively. Pairwise comparisons of mutant allele fractions (MAFs) for samples simultaneously positive for ≥2 mutations revealed an absence of significant differences (<i>p</i> > 0.05), except for the pair of <i>FGFR3</i> vs. <i>PIK3CA</i> (<i>p</i> = 0.03). MAFs were not associated with any clinical and demographic features (<i>p</i> > 0.05), with the only exception being the tumor size: patients with tumors larger than 2.16 cm³ had higher MAFs than the rest (23.4 [1.8; 46.3] vs. 1.6 [0; 24.6] %, respectively, <i>p</i> = 0.02). <b>Conclusions</b>: Upon further validation, the presented tumor DNA detection panel for ddPCR might become a useful tool for diagnostic purposes in UBC.