Discordant fibroblast growth factor receptor 3 (FGFR3) expression between photodynamic diagnosis–positive and –negative bladder cancer lesions: An intra-patient paired analysis

BACKGROUND: 5-Aminolevulinic acid (ALA)-based photodynamic diagnosis (PDD) improves the detection of non-muscle-invasive bladder cancer (NMIBC) during transurethral resection of bladder tumor (TURBT). However, some urothelial carcinomas exhibit no fluorescence (PDD false-negative; FN). The molecular background of FN lesions in human specimens remains insufficiently understood. Therefore, we performed an intra-patient paired comparison between PDD true-positive (TP) and FN lesions coexisting within the same bladder, focusing on immunohistochemical expression profiles, particularly FGFR3. METHODS: We retrospectively reviewed patients who underwent oral ALA-based PDD-TURBT at Kochi University Hospital (January 2018-July 2025). Urothelial carcinomas were classified as TP or FN by intraoperative consensus among ≥3 urologists. Patients harboring both TP and FN lesions were included. Immunohistochemistry for PEPT1, ABCG2, FECH, and FGFR3 was performed on formalin-fixed, paraffin-embedded specimens, scored semi-quantitatively (0-3) by a pathologist, and compared within each patient. RESULTS: Seven cases with paired TP and FN lesions were analyzed. FECH and ABCG2 scores were concordant between TP and FN lesions in all cases. PEPT1 showed discordant scores in 2/7 cases. However, FGFR3 expression was lower in FN than TP lesions in 6 cases, while 1 case showed higher FGFR3 expression in the FN lesion. CONCLUSIONS: In this preliminary exploratory analysis, PDD FN lesions were not uniformly explained by differences in PEPT1/ABCG2/FECH expression alone. Lesion-level discordance in FGFR3 expression may reflect phenotypic heterogeneity within the same bladder and may contribute to fluorescence negativity. Further larger studies integrating molecular alteration status and functional assays are warranted.