Baseline clinical characteristics of PTC patients
We extracted and investigated data of 497 PTC patients from the TCGA database. The patients were randomly assigned into the training cohort or testing cohort. In Table 1, we demonstrated the detailed clinical characteristics (age, sex, vital status, stages, and T/N/M classification) of both cohorts, finding no significant differences between the two groups (P > 0.05).
Table 1
Clinical characteristics of 497 patients with PTC
Variable | Train cohort | Test cohort | P value |
| (n = 249) | (n = 248) | |
Age | | | 0.968 |
< 45 | 112 | 112 | |
≥ 45 | 137 | 138 | |
Sex | | | 0.064 |
Male | 75 | 57 | |
Female | 174 | 193 | |
Vital status | | | 0.617 |
Death | 9 | 7 | |
Alive | 240 | 241 | |
Stages | | | 0.768 |
Ⅰ | 140 | 138 | |
Ⅱ | 28 | 23 | |
Ⅲ | 53 | 61 | |
Ⅳ | 28 | 26 | |
T classification | | | 0.302 |
T1 | 67 | 76 | |
T2 | 92 | 74 | |
T3 | 78 | 85 | |
T4 | 12 | 11 | |
Tx | 0 | 2 | |
N classification | | | 0.166 |
N0 | 107 | 121 | |
N1 | 120 | 99 | |
Nx | 22 | 28 | |
M classification | | | 0.584 |
M0 | 139 | 139 | |
M1 | 3 | 6 | |
Mx | 107 | 103 | |
Selection of differentially expressed miRNAs and candidate diagnostic biomarkers
To select significantly differentially expressed miRNA in the 497 PTC tissues and 59 adjacent normal thyroid tissues (Fig. 1), we performed volcano plot to evaluate miRNA expression variation with the standard of FC > 2 or < 0.5, as well as FDR < 0.05. A total of 237 miRNAs were differentially expressed in the cancerous tissues comparing to the normal tissues, including 172 up-regulated miRNAs and 65 downregulated miRNAs. These 237 significantly differently expressed miRNAs were identified as potential prognostic biomarkers for PTC. To screen out the OS-related miRNAs, univariate cox regression analysis was performed for these significantly differentially expressed miRNAs in the training cohort. Subsequently, we found five miRNAs were distinctly associated with the OS of PTC (Table 2).
Table 2
Univariate cox regression analyses five miRNA were distinctly associated with OS of PTC in train cohort
miRNA | P value | HR | Lower 95%CI | Upper 95%CI |
hsa-miR-138-5p | 0.0001 | 1.002 | 1.001 | 1.004 |
hsa-miR-1179 | 0.0007 | 1.012 | 1.005 | 1.019 |
hsa-miR-138-1-3p | 0.0010 | 1.028 | 1.011 | 1.045 |
hsa-miR-612 | 0.0064 | 1.372 | 1.093 | 1.722 |
hsa-miR-7-2-3p | 0.0077 | 1.011 | 1.003 | 1.019 |
Abbreviations: CI, confidence interval; HR, hazard ratio; PTC, papillary thyroid cancer. |
Construction of the miRNA prognostic signature
To construct the miRNA prognostic signature, these five miRNAs were further selected into LASSO analysis and multivariate cox regression analysis. The lambda value was set using the lambda.min, which is the value of lambda, giving minimum mean cross-validated error. Four miRNAs with non-zero coefficients were defined. The result of the LASSO analysis was shown in Figure S1. We finally managed to established four miRNAs which have independent prognostic effect for PTC in the training cohort based on the LASSO and Cox regression models (Table 3). To reveal the weight of each weighting coefficient of miRNAs clearly, forest figure was presented in Figure S2. We then chose the same median risk score in the two aforementioned independent cohorts as the cutoff point, classifying patients into the low-risk group and the high-risk group. Figure 2 showed the distribution of the miRNA-based risk score, OS, and four miRNAs expression profiles of the training cohort and testing cohort. Kaplan–Meier survival analysis indicated a much worse prognosis (P < 0.001) in the high-risk group (Fig. 3A).
Table 3
Multivariate cox regression analyses of four miRNA were distinctly associated with OS of PTC in train cohort
miRNA | coefficient | P value | HR | Lower 95%CI | Upper 95%CI |
hsa-miR-181a-2-3p | -0.001 | 0.0800 | 1.000 | 1.000 | 1.000 |
hsa-miR-138-5p | 0.003 | 0.0001 | 1.003 | 1.001 | 1.004 |
hsa-miR-424-3p | -0.018 | 0.0590 | 0.982 | 0.964 | 1.001 |
hsa-miR-612 | 0.284 | 0.0242 | 1.329 | 1.038 | 1.702 |
Abbreviations: CI, confidence interval ; HR, hazard ratio; PTC, papillary thyroid cancer. |
In the next, we conducted time-dependent ROC curve analysis to assess the performance of our four miRNAs signature in predicting PTC prognosis. The AUC values of the four miRNAs signature at five years were 0.937 and 0.812 in the training cohort and testing cohort, respectively (Fig. 3B). To make the prognostic miRNAs signature more convenient in clinical practice, these four-miRNAs based nomogram was established (Fig. 4A). Furthermore, calibration plots of these four miRNAs based prognostic model showed well compactness in the training cohort and testing cohort at 3-year survival and 5-year survival, respectively, which indicated good calibration ability(Fig. 4B and 4C).
The four miRNAs signature as an independent prognostic factor of OS
The predictive effect of the four miRNAs signature on OS in consideration of clinicopathological features were evaluated adopting the univariate analysis and multivariate Cox regression analysis. Multivariate Cox regression analysis showed that the four miRNAs signature was an independent prognostic factor associated with the OS of PTC patients (Table 4).
Table 4
Univariate and multivariate cox regression analyses of the four miRNA signature and clinicopathologic factors in the entire set
| Univariate analysis | Multivariate analysis |
| HR (95%CI) | P | HR (95%CI) | P |
Age (< 45 vs ≥ 45) | 0.013 (0.000-0.756) | 0.036 | - | - |
Stage (Ⅰ/Ⅱ vs Ⅲ/Ⅳ) | 0.141 (0.045–0.439) | 0.001 | - | - |
Sex | 2.029 (0.734–5.613) | 0.173 | - | - |
Four miRNA signature (high risk vs low risk) | 8.625 (1.956–38.03) | 0.004 | 6.186 (1.405–27.24) | 0.016 |
Abbreviations: CI, confidence interval; HR, hazard ratio; PTC, papillary thyroid cancer; |
Target prediction and function analysis
The target genes of the selected four miRNAs, hsa-miR-181a-2-3p, hsa-miR-138-5p, hsa-miR-424-3p, and hsa-miR-612, were predicted by TargetScan and miRDB. Then, the biological roles of the overlapped target genes were assessed by the enrichment analysis. The GO biological processes were mainly enriched in the regulation of nucleobase, nucleoside, nucleotide, and nucleic acid metabolism, transport, regulation of gene expression, epigenetic, and cell adhesion (Table 5). In addition, the KEGG pathways were remarkably enriched in the integrin family cell surface interactions, beta1 integrin cell surface interactions, proteoglycan syndecan-mediated signaling events (Table 6).
Table 5
The significant enriched GO biological processes of target genes
Term | Count | Fold enrichment | P-value |
Regulation of nucleobase, nucleoside, nucleotide and nucleic acid metabolism | 291 | 1.228 | < 0.001 |
Transport | 127 | 1.247 | 0.005 |
Regulation of gene expression, epigenetic | 12 | 2.171 | 0.008 |
Cell adhesion | 12 | 2.653 | 0.001 |
Table 6
The significant enriched KEGG pathways of target genes
Term | Count | Fold enrichment | P value |
Integrin family cell surface interactions | 149 | 1.265 | < 0.001 |
Beta1 integrin cell surface interactions | 147 | 1.273 | < 0.001 |
Proteoglycan syndecan-mediated signaling events | 146 | 1.2670 | < 0.001 |
PAR1-mediated thrombin signaling events | 145 | 1.306 | < 0.001 |
Thrombin/protease-activated receptor (PAR) pathway | 145 | 1.305 | < 0.001 |
VEGF and VEGFR signaling network | 145 | 1.301 | < 0.001 |
Alpha9 beta1 integrin signaling events | 145 | 1.300 | < 0.001 |
ErbB receptor signaling network | 145 | 1.294 | < 0.001 |
Sphingosine 1-phosphate (S1P) pathway | 145 | 1.294 | < 0.001 |
TRAIL signaling pathway | 145 | 1.277 | < 0.001 |