Levels of tumor biomarkers in the BTC, HCC, CHC, BBD, and HP groups
To investigate the expression levels of different tumor markers in different types of populations, the preoperative expression levels of CA50, CA19-9, AFP, and CEA in BTC patients were measured and compared with those of non-BTC controls (Figure 2). The median levels of serum CA50 in the BTC, HCC, CHC, BBD and HP groups were 61.5 U/ml, 13.6 U/ml, 7.7 U/ml, 5.6 U/ml and 5.9 U/ml, respectively. The median levels of serum CA19-9 in the BTC, HCC, CHC, BBD and HP groups were 120.3 U/ml, 11.2 U/ml, 17.3 U/ml, 7.7 U/ml and 9.7 U/ml, respectively. The median levels of serum AFP in the above groups were 3.1 ng/ml, 15.1 ng/ml, 14.0 ng/ml, 2.8 ng/ml and 2.3 ng/ml, respectively. The median levels of serum CEA in the above groups were 3.3 ng/ml, 2.5 ng/ml, 2.4 ng/ml, 1.7 ng/ml and 1.6 ng/ml, respectively (Table 1, Figure 2). The levels of serum CA50, CA19-9, and CEA in the BTC patients were higher than those in the HCC, CHC, BBD, and HP patients, and the difference was significant (P <0.001) (Table 1).
In addition, correlation analysis of CA50 with other tumor markers is presented in Figure 3. The serum CA50 was significantly correlated with serum CA19-9. The R-values in BTC, HCC, CHC, BBD, and HP were 0.85, 0.62, 0.76, 0.89, and 0.95, respectively (Figure 3A). However, the serum CA50 was not significantly correlated with serum AFP or CEA, and the R-values were all small in the above patients (Figure 3B and Figure 3C).
Therefore, the levels of serum CA50, CA19-9, and CEA in the BTC patients were higher than those in HCC, CHC, BBD, and HP patients. In addition, the levels of serum CA50 and CA19-9 were significantly correlated in BTC, CHC, BBD, and HP patients.
Diagnostic values of serum tumor markers and the model in BTC patients
A total of 1121 persons were randomly divided into the train cohort and the validation cohort according to 6: 4 (673: 448). There were not significant statistical differences in age, sex, different levels of serum tumor markers, maximum tumor, and study population between the train cohort and the validation cohort (Table 2).
Comparing BTC and non-BTC, the best cut-off value of the single serum CA50 level was 24.875 U/ml (train cohort: AUC 0.841, 95% CI 0.808-0.875, specificity 92.2%, sensitivity 68.0%; validation cohort: AUC 0.833, 95% CI 0.789-0.876, specificity 91.7%, sensitivity 65.6%). The best cut-off value of CA19-9 was 31.680 U/ml (train cohort: AUC 0.851, 95% CI 0.818-0.885, specificity 93.2%, sensitivity 71.9%; validation cohort: AUC 0.859, 95% CI 0.819-0.899, specificity 92.5%, sensitivity 69.8%). The best cut-off value of AFP was 3.105 ng/ml (train cohort: AUC 0.476, 95% CI 0.430-0.521, specificity 52.6%, sensitivity 51.9%; validation cohort: AUC 0.498, 95% CI 0.442-0.553, specificity 57.3%, sensitivity 46.4%). And the best cut-off value of CEA was 3.230 ng/ml (train cohort: AUC 0.715, 95% CI 0.673-0.757, specificity 78.6%, sensitivity 53.1%; validation cohort: AUC 0.704, 95% CI 0.653-0.756, specificity 80.4%, sensitivity 48.8%) (Table 3, Figure 4). The AUC of serum CA19-9 and CA50 were higher than that of AFP and CEA, and serum CA50 and CA19-9 had a better specificity and positive LR. The accuracy, positive predictive value (PPV), negative predictive value (NPV), positive likelihood ratio (LR) and negative LR of the different tumor markers are also shown in Table 3. In addition, we built a clinical diagnostic model by combining CA50, CA19-9 and AFP, and the AUCs of the MODEL 1 was 0.885 (train cohort: 95% CI 0.856-0.915, specificity 93.9%, sensitivity 74.3%) and 0.879 (validation cohort: 95% CI 0.841-0.917, specificity 92.8%, sensitivity 75.9%), which was higher than that of the above serum tumor markers alone (Figure 4A, Figure 4B). The results of DCAs also indicated that the MODEL 1 could add more benefit than the “treat none” and “treat all” (Figure 4C, Figure 4D).
In the MODEL 1, we used the following formula: logit= -1.83862 +0.02204*CA50 +0.01214*CA199 -0.00245*AFP. The nomogram of the MODEL 1 was shown in Figure 5.
Therefore, CA50 is a potential tumor marker for the screening and diagnosis of BTC patients. Distinguish BTC and non-BTCs patients, serum CA50 and CA19-9 had a better specificity and positive LR than those of AFP and CEA. The AUCs of the MODEL 1 by combining CA50, CA19-9 and AFP were higher than those of the single serum tumor markers.
Diagnostic values of different tumor markers and the model in iCCA patients
A total of 392 persons were randomly divided into the train cohort and the validation cohort according to 6: 4 (235: 157). There were not significant statistical differences in age, sex, different levels of serum tumor markers, maximum tumor, and study population between the train cohort and the validation cohort (Table 4).
Distinguishing iCCA and HCC, the best cut-off value of serum CA50 was 52.995 U/ml (train cohort: AUC 0.752, 95% CI 0.688-0.816, specificity 93.5%, sensitivity 58.6%; validation cohort: AUC 0.698, 95% CI 0.612-0.783, specificity 94.4%, sensitivity 48.8%). And the best cut-off value of serum CA19-9 was 52.700 U/ml (train cohort: AUC 0.834, 95% CI 0.781-9.887, specificity 90.7%, sensitivity 68.0%; validation cohort: AUC 0.781, 95% CI 0.708-0.854, specificity 91.6%, sensitivity 58.8%). The best threshold of AFP was 6.750 ng/ml (train cohort: AUC 0.761, 95% CI 0.697-0.825, specificity 58.4%, sensitivity 85.6%; validation cohort: AUC 0.702, 95% CI 0.614-0.790, specificity 59.4%, sensitivity 84.2%). And the best threshold of CEA was 3.325 ng/ml (train cohort: AUC 0.672, 95% CI 0.595-0.748, specificity 68.0%, sensitivity 61.1%; validation cohort: AUC 0.550, 95% CI 0.450-0.651, specificity 53.9%, sensitivity 50.6%) (Table 5, Figure 6). The accuracy, PPV, NPV, positive LR and negative LR of the different tumor markers are also shown in Table 5. In addition, we also built a clinical diagnostic model by combining CA50, CA19-9 and AFP, and the AUCs of the MODEL 2 was 0.893 (train cohort: 95% CI 0.853-0.933, specificity 96.0%, sensitivity 68.6%) and 0.872 (validation cohort: 95% CI 0.818-0.927, specificity 94.2%, sensitivity 64.6%), which was higher than that of the above tumor marker alone (Figure 6A, Figure 6B). The results of DCAs also indicated that the MODEL 2 could add more benefit than the “treat none” and “treat all” (Figure 6C, Figure 6D). In the MODEL 2, we used the following formula: logit= -0.75580 +0.00766*CA50 +0.01554*CA19.9 -0.00999*AFP. The nomogram of the MODEL was shown in Figure 7.
Therefore, compared to CA19-9, AFP, and CEA, serum CA50 had a better specificity and positive LR in iCCA patients. The AUCs of the MODEL 2 by combining CA50, CA19-9 and AFP were higher than those of the single serum tumor markers.
Clarification of the relationship between different tumor marker levels and BTC location
BTCs were classified into five types, including iCCA, pCCA, dCCA, GBC, and VPC, based on their anatomic location. A total of 458 BTC patients were classified, 214 with iCCA, 62 with pCCA, 66 with dCCA, 78 with GBC, 38 with VPC. The overall distribution of the different tumor markers in different locations of BTC was shown in Supplementary Figure 1. The median levels of serum CA50 in the iCCA, pCCA, dCCA, GBC and VPC patients were respectively 66.5 U/ml, 95.3 U/ml, 61.3 U/ml, 30.9 U/ml and 77.7 U/ml, respectively. The median levels of serum CA19-9 in the iCCA, pCCA, dCCA, GBC and VPC patients were respectively 134.4 U/ml, 231.9 U/ml, 62.1 U/ml, 62.5 U/ml, and 104.8 U/ml respectively (Supplementary Table 1). The median levels of serum AFP in the iCCA, pCCA, dCCA, GBC and VPC patients were respectively 3.2 U/ml, 3.4 U/ml, 2.9 U/ml, 2.4 U/ml and 2.5 U/ml. And the median levels of serum CEA in the above locations were 3.5 ng/ml, 3.7 ng/ml, 2.9 ng/ml, 2.3 ng/ml and 3.5 ng/ml, respectively. The serum CA19-9, AFP, and CEA values were significantly different at different locations of BTCs (P =0.020, P =0.026, P =0.001). (Supplementary Figure 1, Supplementary Table 1).
Therefore, the levels of serum AFP, CA19-9 and CEA were correlated with the location of BTCs. The serum CA50 and CA19-9 levels were expressed at higher levels in pCCA than in iCCA, dCCA, GBC and VPC.
Clarification of the relationship between different tumor marker levels and the degree of jaundice
Based on the total bilirubin levels (TBIL), patients with BTC were divided into five groups: no jaundice group (TBIL <17.1 μmol/L), recessive jaundice group (TBIL: 17.1-34.2 μmol/L), mild jaundice group (TBIL: 34.3-171.0 μmol/L), moderate jaundice group (TBIL: 172.0-342.0 μmol/L) and severe jaundice group (TBIL >342.0 μmol/L) (Supplementary Figure 2). The median serum CA50 levels in the above five groups were 28.5 U/ml, 65.3 U/ml, 80.7 U/ml, 132.0 U/ml, 312.8 U/ml, and the median serum CA19-9 levels in the above five groups were 53.6 U/ml, 121.4 U/ml, 143.6 U/ml, 173.8 U/ml, 522.9 U/ml. The serum levels of both CA50 and CA19-9 increased with the severity of jaundice, and the difference was statistically significant (P <0.001, P =0.010). There was no significant difference between the serum CEA and AFP levels and the degree of jaundice in different groups (P =0.721, P =0.583) (Supplementary Table 2, Supplementary Figure 2).
Therefore, the serum CA50 and CA19-9 levels increased with the degree of jaundice.
Clarification of the relationship between different tumor marker levels and the degree of pathological pattern
Based on the pathological examination results, patients with BTC were divided into four groups: poorly differentiated adenocarcinoma, moderately differentiated adenocarcinoma, High differentiated adenocarcinoma, and other types (Supplementary Figure 3). Other types including squamous cell carcinoma, adeno-squamous carcinoma, neuroendocrine carcinoma and so on. The median serum CA50 levels in the above four groups were 66.6 U/ml, 63.8 U/ml, 35.2 U/ml, 46.3 U/ml, and the median serum CA19-9 levels in the above four groups were 134.4 U/ml, 102.9 U/ml, 60.4 U/ml, 110.1 U/ml. The serum levels of CA50 and CA19-9 were highest in the poorly differentiated adenocarcinoma. The serum levels of CA19-9 increased with the severity of jaundice (P =0.048). There was no significant difference between the serum CA50, CEA, and AFP levels and the degree of jaundice in different groups (P =0.358, P =0.795, P =0.294) (Supplementary Table 3, Supplementary Figure 3).
Therefore, the serum CA19-9 levels were obviously higher in the poorly differentiated adenocarcinoma than in the high differentiated adenocarcinoma in BTCs.