Differences in SCN4B expression between ccRCC and normal tissues
To confirm the association between SCN4B expression and ccRCC, we collected gene expression data for 541 ccRCC patients and 72 normal subjects from the TCGA database. The data revealed significantly higher SCN4B expression in ccRCC patients compared to normal subjects (P < 0.001, Fig. 1A). A paired comparison analysis of 72 cancer patients and 72 normal controls corroborated these findings (P < 0.001, Fig. 1B). ROC curve analysis demonstrated that SCN4B could effectively differentiate between tumor and non-tumor tissues, with an area under the curve of 0.835 (CI = 0.798–0.871) (Fig. 1C).
SCN4B expression was examined across 33 common tumor types (Fig. 1D), showing significant overexpression in seven types, including lymphoid neoplasm diffuse large B-cell lymphoma (DLBC) (P < 0.001), ccRCC (KIRC) (P < 0.001), acute myeloid leukemia (LAML) (P < 0.001), liver hepatocellular carcinoma (LIHC) (P < 0.001), ovarian serous cystadenocarcinoma (OV) (P < 0.001), pancreatic adenocarcinoma (PAAD) (P < 0.001), and thymoma (THYM). Conversely, SCN4B was significantly underexpressed in 19 tumor types, including adrenocortical carcinoma (ACC) (P < 0.001), bladder urothelial carcinoma (BLCA) (P < 0.001), breast invasive carcinoma (BRCA) (P < 0.001), cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC) (P < 0.001), colon adenocarcinoma (COAD) (P < 0.001), esophageal carcinoma (ESCA) (P < 0.001), glioblastoma multiforme (GBM) (P < 0.001), head and neck squamous cell carcinoma (HNSC) (P < 0.01), kidney renal papillary cell carcinoma (KIRP) (P < 0.001), brain lower grade glioma (LGG) (P < 0.001), lung adenocarcinoma (LUAD) (P < 0.001), lung squamous cell carcinoma (LUSC) (P < 0.001), prostate adenocarcinoma (PRAD) (P < 0.001), rectum adenocarcinoma (READ) (P < 0.001), stomach adenocarcinoma (STAD) (P < 0.001), testicular germ cell tumors (TGCT) (P < 0.001), thyroid carcinoma (THCA) (P < 0.001), uterine corpus endometrial carcinoma (UCEC) (P < 0.001), and uterine carcinosarcoma (UCS) (P < 0.001).
To validate our conclusions, independent samples from two separate studies were analyzed for SCN4B expression differences (all samples were from human kidney tissue). The data from the TCGA database (Fig. 1E) included 72 normal kidney tissues and 541 ccRCC tissues, showing a log fold change of 1.955 (P < 0.001). Data from a published study by John A Copland (Fig. 1F) included 72 normal kidney tissues and 72 ccRCC tissues, showing a log fold change of 1.903 (P < 0.001).
Relationship between SCN4B expression and clinicopathologic characteristics of ccRCC
Baseline data for 541 ccRCC patients from the TCGA database were statistically analyzed (Table 1). The cohort was divided into two groups: 270 patients with relatively low SCN4B expression and 271 with relatively high SCN4B expression. Significant differences were observed in sex (P = 0.002), while no significant differences were noted in age (P = 0.576). Significant differences were found in T stage (P < 0.001) and M stage (P < 0.001), but not in N stage (P = 0.061). Differences were also significant in pathological stage (P < 0.001).
Logistic regression analysis (Table 2) revealed significant associations between SCN4B expression and clinicopathological characteristics of ccRCC. No significant differences were found in age (P = 0.576) and N stage (P = 0.072). Significant differences were observed between stages T3 and T4 compared to stages T1 and T2 (P < 0.001). Similarly, significant differences were found between stages III and IV compared to stages I and II (P < 0.001). The analysis also revealed a significant difference between M1 and M0 stages (P < 0.001).
Table 1 Correlation between SCN4B expression and clinicopathologic characteristics of ccRCC
Table 2 SCN4B expression associated with clinicopathologic characteristics(logistic
To further validate the relationship between SCN4B expression and pathological stages of ccRCC, we analyzed SCN4B expression in samples from different pathological stages. The results showed significantly higher SCN4B expression in ccRCC samples at stages T1, T2, and T3 compared to normal kidney tissues, with significant differences between stages T1 and T2, T3, and T4 (Fig. 2A). SCN4B expression was significantly higher in N0 stage compared to normal tissues, with significant differences between stages N0 and N1 (Fig. 2B). SCN4B expression was also significantly higher in M stages compared to normal tissues, with significant differences between stages M0 and M1 (Fig. 2C). Additionally, SCN4B expression was significantly higher in all four pathological stages of ccRCC compared to normal tissues, with significant differences between stages I and II, as well as stages I and III (Fig. 2D).
Role of SCN4B expression in the survival of patients with ccRCC
Kaplan–Meier survival curves were used to evaluate the prognostic value of SCN4B expression in ccRCC. The overall survival (OS) curve showed that patients with high SCN4B expression had a significantly higher survival rate compared to those with low expression (HR = 0.57, 95% CI: 0.42–0.78, P < 0.001) (Fig. 3A). A similar result was observed for the progression-free interval (PFI) (HR = 0.50, 95% CI: 0.36–0.69, P < 0.001) (Fig. 3B). To better predict recurrence-free survival after treatment, a Cox regression analysis was performed with PFI as a dependent variable (Table 3). Univariate analysis showed a significant correlation between pathological stage and PFI, including pathologic T1 and T2 vs. T3 and T4 (HR = 4.569 (3.306–6.314), P < 0.001), pathologic N0 vs. N1 (OR = 3.697 (1.899–7.198), P < 0.001), sex male vs. female (HR = 1.476 (1.043–2.090), P < 0.001), pathologic M0 vs. M1 (OR = 9.081 (6.554–12.582), P < 0.001), and pathologic stage I and II vs. stage III and IV (OR = 6.877 (4.813–9.826), P < 0.001). Multivariate analysis indicated that pathologic M0 vs. M1 (OR = 4.062 (2.439–6.765), P < 0.001) and pathologic stage I and II vs. stage III and IV (OR = 3.983 (1.676–9.463), P = 0.002) were significantly associated with PFI.
Table 3 Univariate and multivariate Cox regression analyses of prognostic factors for PFI in ccRCC
Correlation between SCN4B expression and immune inffltration
Using the ssGSEA algorithm, we assessed the correlation between SCN4B expression and 24 immune cell types related to immune infiltration. Visualization (Fig. 4A) showed the correlation between immune cell enrichment and SCN4B, with circle size representing the correlation strength and color indicating the P-value. The top three immune cells with the strongest correlation and significant P-values were selected for further analysis. SCN4B expression was positively correlated with NK cell infiltration (R = 0.415, P < 0.001), mast cell infiltration (R = 0.405, P < 0.001), and pDC infiltration (R = 0.381, P < 0.001) (Fig. 4B, C, and D). Statistical analysis revealed significantly higher infiltration levels of NK cells, mast cells, and pDC in samples with high SCN4B expression compared to those with low expression (Fig. 4E, F, and G).