BC has become one of the most common malignancy due to its increasing incidence and high recurrence rates . Therefore, early diagnosis and prognosis prediction need to be taken seriously. It is common knowledge that the accumulation of genetic alteration in tumor-related genes is necessary for the development and progress of carcinogenesis . Therefore, our study concentrated on addressing the clinical significance of mutated genes with highly frequency for bladder cancer.
Single markers have been used clinically for many years, but there are still shortcomings such as low sensitivity and specificity. So far, numerous studies have demonstrated that combination markers could improve sensitivity and specificity and better predict the prognosis of patients [33, 34]. Furthermore, given the heterogeneity of bladder cancer, it is unlikely to identify its progression by a single marker. This underlines the importance of biomarker combinations . In this study, we analyzed the whole mutation profile and identified 23 mutated genes which had a clearly correlation with the prognosis of bladder patients. Furthermore, we found this mutation signature has high accuracy by time-dependent ROC analysis and was an independent indicator by multivariable Cox regression analysis.
Besides, more and more researches have demonstrated that combined molecular with clinical features have higher predictive ability than single biomarker [36, 37]. Thus, nomogram and DCA analysis were established by combining risk score with clinical features involving TNM stage, T stage, N stage, tumor status and lymphovascular invasion. The results suggested that combined parameters performs better in survival prediction for bladder patients and has good clinical application. Our findings provide a superior and helpful prognostic biomarker for bladder patients.
Recent evidence has implicated bladder exist four mutational signatures, including signature 1B, signature 2, signature 5 and signature 13. Both Signature 2 and 13 are mainly featured by C > T as well as C > G and have a close connection with the APOBEC families of cytidine deaminases. In our study, we also observed alteration are mainly featured by C > T together with C > G. APOBEC enzymes usually play essential role in innate immune responses, embracing target retroviruses, demonstrating that there are interrelated among immunity mutagenesis, and viral infection in the progression of cancer development . Based on the similarity of the sequence background of cytosine mutations caused by APOBEC enzymes in experimental systems, APOBEC1, APOBEC3A and APOBEC3B appear to play a greater role in human cancer than other members of the family. Hence, we investigated the expression of APOBEC1, APOBEC3A and APOBEC3B and their expression based on clinical characteristics in bladder. APOBEC1 and APOBEC3A are not significantly differential expressed in bladder tumor (Additional file 3). And we found APOBEC3B is not only highly expressed in tumor, but also its higher expression is related to advanced TNM stage and higher N stage (Fig. 7). Thus, we further explored relationship between our mutation signature and APOBEC3B and found patients with high risk score have higher APOBEC3B expression, suggesting our signature is a reliable predictor to estimate survival of bladder patients.
It is well known that the epithelial-mesenchymal transition (EMT) process plays a significant role in embryonic development as well as tissue repair and tightly associated with cancer metastasis and invasiveness including bladder cancer [39, 40]. In human, hedgehog homologs was divided into three types including sonic hedgehog (Shh), desert hedgehog (Dhh) and Indian hedgehog (Ihh) . Shh is currently the best studied of these three homologs, . Previous study suggested that sonic hedgehog (Shh) is a crucial element for the development and progression of bladder cancer . The PI3K-AKT signaling pathway, a well-known cancer-related signaling pathway, has close relationships with cell growth, cell cycle, survival as well as metastasis in various cancer including bladder cancer [44, 45]. Therefore, it is highly possible that these selected genes may influence the bladder progression through these pathways. Besides, interferon is a cytokine produced by monocytes and lymphocytes. It is divided into three types: α, β and γ. Many studies have shown that interferon (especially α-interferon and γ-interferon) has an obvious anti-cell proliferation effect . Therefore, low-risk patients have a better prognosis and reduce mortality through these immune response and inflammatory response.
It has been reported that some of the screened genes play an essential role be in the tumorigenesis, including bladder cancer. For example, NCOR1 gene was found to be high frequently mutation in bladder cancer. In our study, NCOR1 is not only a highly mutated gene in bladder cancer but also associated with better prognosis of patients. Another candidate, bladder patients with BRCA2 gene mutation have a better prognosis . In our study, we also observed mutated BRCA2 exerts a protective role. However, when combined with other mutated genes, it played a risky role for bladder patients. As for the rest of mutated genes, such as AHNAK2, RYR2, DCHS2, USH2A, RP1L1 and so on were found to be mutated in various cancer and diseases [48–55]. Although the effect of these genes' mutation on bladder cancer were previously unclear, our findings indicated that these genes were associated with patients' survival and deserve further investigations in bladder cancer.