Comparative analysis of the mutational status of non-muscle-invasive and muscle-invasive urothelial carcinoma

Aim. To identify mutational profile differences of non-muscle-invasive (NMIUC) and muscle-invasive urothelial carcinoma (MIUC) of the bladder, assessed through isolating alterations in deoxyribonucleic (DNA) and ribonucleic (RNA) acids by a next-generation sequencing (NGS) method using a panel of 523 genes.

Materials and methods. Tumor tissue and medical data of 72 patients with histologically confirmed bladder UC were studied. NMIUC was diagnosed in 40 (55.6%) patients, and MIUC in 32 (44.4%) patients. In 25 (34.7%) samples the tumor grade was assessed as low: 24 (33.3%) with NMIUC and 1 (1.4%) with MIUC, and in 47 (65.3%) as high: 16 (22.2%) with NMIUC, 31 (43.1%) with MIUC. In isolated tumor cells DNA and RNA alterations were detected by NGS using a panel of 523 genes.

Results. NMIUC, compared to MIUC, was characterized by a lower median mutational burden (9.9 mut/Mb vs. 11.8 mut/Mb, respectively; p=0.037) and was associated with a higher rate of mutations of the FGFR/FGF (p=0.059) and STAG2/IRF (p=0.055) signaling pathways genes, as well as the FGFR3 (p=0.001) and STAG2 (p=0.026) genes with a lower rate of aberrations of the p53 signaling pathway genes (p=0.005), TP53 (p=0.001) and FGF4 (p=0.057). The low grade NMIUC samples had a lower rate of high mutational burden (vs. high grade NMIUC, p=0.004; vs high grade MIUC, p=0.067) and were also associated with a higher rate of FGF/FGFR signaling pathway gene mutations (vs. high grade MIUC, p<0.0001; vs. high grade NMIUC, p<0.0001), mainly due to FGFR3 alterations (vs. high grade NMIUC; p<0.0001; vs. high grade MIUC; p<0.0001). Low grade NMIUC, compared to high grade MIUC, had a higher rate of PIK3CA (p=0.027) and KDM6A (p=0.001) mutations. The mutational profile of high grade NMIUC and high grade MIUC did not differ significantly. High grade MIUC, compared to low grade NMIUC had a higher rate of mutations of the p53 pathway genes (p=0.008), including TP53 (p=0.001), and a significantly lower rate of alterations of the FGF/FGFR signal pathway genes (p<0.0001), including FGFR3 (p<0.0001), as well as the STAG2/IRF pathway genes (p=0.035) and the PIK3CA gene (p=0.027).

Conclusion. Differences of the histological structure and natural history of low grade NMIUC, high grade NMIUC, and high grade MIUC are due to significant differences in their mutational status. NMIUC has a high rate of mutations in genes of the FGF/FGFR signaling pathway and inactivating mutations in STAG2 and KDM6A genes. MIUC typically has driver mutations that inactivate the p53 signal pathway. High grade NMIUC has alterations typical for both NMIUC (FGF/FGFR pathway gene mutations) and MIUC (p53 pathway gene mutations).