Characteristics of the study population
Participants were categorized into four groups based on the diagnosis as NL (n=609, 30.6%), OC (n=145, 7.3%), PB (n=314, 15.7%), and PDAC (n=923, 46.4%). The NL, OC, and PB groups were together clubbed into the non-PDAC group (n=1068, 53.6%). Demographics of the participants in the non-PDAC and PDAC groups are summarized in Table 4. Significant differences were observed in age (Non-PDAC; 55.5 ± 12.0 versus PDAC; 63.1 ± 9.9 years, p < 0.001), sex ratio (females: n=474, 44.4% vs. males: n=561, 60.8%, p < 0.001), body mass index (23.6 ± 3.2 versus 22.9 ± 3.0 kg/m2, p = 0.001), level of initial CA 19-9 (19.0 ± 98.6 versus 679.0 ± 1348.9 U/ml, p < 0.001), and level of LRG1, TTR, CA 19-9 in automated ELISA triple marker panel between the non-PDAC and PDAC groups. Levels of LRG1 and CA 19-9 were higher in the PDAC group than in the non-PDAC group, whereas the level of TTR was lower in the PDAC group than in the NL and OC groups.
Table 4. Demographics of study population
|
Total
|
Non-PDAC
|
Non-PDAC
|
PDAC
|
p-value
(Non-PDAC versus PDAC)
|
NL
|
OC
|
PB
|
Number
|
1991 (100.0)
|
609 (30.6)
|
145 (7.3)
|
314 (15.7)
|
1068 (53.6)
|
923 (46.4)
|
|
Age, years
|
59.0 ± 11.7
|
56.4 ± 11.0
|
55.2 ± 11.5
|
53.9 ± 13.8
|
55.5 ± 12.0
|
63.1 ± 9.9
|
< 0.001
|
Sex
|
|
|
|
|
|
|
< 0.001
|
Male
|
1035 (52.0)
|
322 (52.9)
|
37 (25.5)
|
115 (36.6)
|
474 (44.4)
|
561 (60.8)
|
|
Female
|
956 (48.0)
|
287 (47.1)
|
108 (74.5)
|
199 (63.4)
|
594 (55.6)
|
362 (39.2)
|
|
BMI, kg/m2
|
23.3 ± 3.1
|
23.8 ± 2.9
|
23.3 ± 3.3
|
23.2 ± 3.8
|
23.6 ± 3.2
|
22.9 ± 3.0
|
0.001
|
Initial
CA 19-9,
U/ml
|
|
11.7 ± 33.3
|
61.7 ± 261.9
|
14.6 ± 23.7
|
19.0 ± 98.6
|
679.0 ± 1348.9
|
< 0.001
|
Initial CEA,
ng/ml
|
|
1.2 ± 0.8
|
26.6 ± 137.2
|
2.0 ± 3.2
|
7.4 ± 67.2
|
29.6 ± 231.5
|
0.087
|
Automated ELISA triple marker panel*
|
LRG1,
ng/ml
|
|
11324 (8348-16281)
|
11427 (8531-15321)
|
9351
(7341-12585)
|
10697 (7909-15138)
|
16836 (11182-25638)
|
< 0.001
|
TTR,
ng/ml
|
|
286200 (154548-432460)
|
302800 (254720-342560)
|
151525 (127697-215568)
|
227910 (146600-365920)
|
150112 (123266-230000)
|
< 0.001
|
CA 19-9,
U/ml
|
|
11.0
(6.5-18.8)
|
10.6
(7.9-17.3)
|
10.8
(5.3-21.1)
|
10.8
(6.6-19.2)
|
118.6
(26.5-537.9)
|
< 0.001
|
Data are expressed as n (%) or mean (standard deviation) unless indicated otherwise; *values are median (25 percentile to 75 percentile)
PDAC, pancreatic ductal adenocarcinoma; NL, normal; OC, other cancer; PB, pancreatic benign; BMI, body mass index; CEA, carcinoembryonic antigen; CA, carbohydrate antigen; ELISA, enzyme-linked immunosorbent assay; LRG, leucine rich alpha 2 glycoprotein; TTR, transthyretin
Diagnostic model and determining cutoff value
An LR-based prediction model was created using NL and PDAC data from an automated multi-panel ELISA kit. The five covariates used to create the LR model were sex, age, and the three biomarkers TTR, CA 19-9, and LRG1. The fitted LR model is represented as follows:
Through the model thus obtained, the predicted value of PDAC incidence for each sample of the training data was obtained and classified into low, intermediate, and high-risk groups using two thresholds (Figure 2a and b). In order to establish the feasibility for clinical use along with better performance, the optimal threshold combination was evaluated. We checked the cutoff values from 85% to 95%. Considering the mean of the four measures, and the sample numbers of low-, intermediate -, and high-risk groups, the threshold combination of 0.22 and 0.88 when all four measure values exceeded 90% were selected (Table 5). The mean of the four measures at this time was 92.2989, and the values of PPV, NPV, Sen, and Spe were 94.1177, 90.4040, 93.8111, and 90.8629, respectively. At threshold combinations of 0.22 and 0.88, the cutoff was 90%, and the number of samples in the high-, intermediate-, and low-risk groups were 306, 569, and 198, respectively.
Table 5. Comparison of measures and number of risk groups from various data set at cut-off 90%
Data set
|
Training
|
Test
(NL vs PDAC)
|
Test
(OC vs PDAC)
|
Test
(PB vs PDAC)
|
Test
(non-PDAC vs PDAC)
|
PPV
|
94.1177
|
93.9850
|
93.2836
|
88.6525
|
79.1139
|
NPV
|
90.4040
|
92.2222
|
91.5663
|
91.7647
|
97.1312
|
Sen
|
93.8111
|
94.6970
|
94.6970
|
94.6970
|
94.6970
|
Spe
|
90.8629
|
91.2088
|
89.4118
|
82.9787
|
87.7778
|
measures
mean
|
92.2989
|
93.0282
|
92.2397
|
89.5232
|
89.680
|
High
|
306
|
133
|
134
|
141
|
158
|
Intermediate
|
569
|
236
|
204
|
364
|
516
|
Low
|
198
|
90
|
83
|
85
|
244
|
PDAC, pancreatic ductal adenocarcinoma; NL, normal; OC, other cancer; PB, pancreatic benign; PPV, positive predictive values; NPV, negative predictive values; Sen, sensitivity; Spe, specificity
Verification using various types of test data sets
To evaluate the performance of the predictive model derived from the training data set, it was verified using the test data. During this, by using the PB and OC types data in addition to NL and PDAC, it was demonstrated that the model had reliable performance prediction ability even when various types of data were provided. First, during modeling using training data, four measure values at various threshold combinations and sample numbers of low -, intermediate -, and high-risk groups were identified. It was found that at the threshold combination of 0.22 and 0.88, which was the optimal threshold combination, the cutoff value was 89.680. This was not significantly different from 92.1989 when training data was used (p = 0.573) (Table 6). The values of PPV, NPV, Sen, and Spe were 79.1139, 97.1312, 94.6970, and 87.7778, respectively, showing an overall good performance except for the PPV (Table 6).
Table 6. Cut-off values of measures, threshold change and number of risk groups from test data set
measures
> cut-off
|
95%
|
94%
|
93%
|
92%
|
91%
|
90%
|
89%
|
88%
|
87%
|
86%
|
85%
|
|
0.09
|
0.12
|
0.14
|
0.16
|
0.21
|
0.22
|
0.25
|
0.26
|
0.29
|
0.3
|
0.32
|
|
0.96
|
0.94
|
0.92
|
0.89
|
0.89
|
0.88
|
0.87
|
0.86
|
0.82
|
0.8
|
0.79
|
PPV
|
84.2857
|
86.6667
|
83.6207
|
80.2817
|
80.2817
|
79.1139
|
76.7857
|
75.9777
|
72.9730
|
71.4876
|
70.2381
|
NPV
|
99.0741
|
98.6014
|
98.2456
|
98.4375
|
97.0086
|
97.1312
|
96.7626
|
96.7972
|
95.5128
|
95.6386
|
94.9704
|
Sen
|
98.3333
|
97.50
|
97.0
|
97.4359
|
94.2149
|
94.697
|
93.4783
|
93.7931
|
92.0455
|
92.5134
|
91.2371
|
Spe
|
90.6780
|
92.1569
|
89.8396
|
87.0968
|
89.0196
|
87.7778
|
87.3377
|
86.3492
|
83.2402
|
81.6489
|
81.0606
|
measures mean
|
93.0928
|
93.7312
|
92.1765
|
90.8130
|
90.1312
|
89.680
|
88.5911
|
88.2293
|
85.9429
|
85.3221
|
84.3766
|
High
|
70
|
90
|
116
|
142
|
142
|
158
|
168
|
179
|
222
|
242
|
252
|
Intermediate
|
740
|
685
|
631
|
584
|
542
|
516
|
472
|
458
|
384
|
355
|
328
|
Low
|
108
|
143
|
171
|
192
|
234
|
244
|
278
|
281
|
312
|
321
|
338
|
Performance comparison by various cut-off values and verifying the performance of a predictive model using all test data set.
PPV, positive predictive values; NPV, negative predictive values; Sen, sensitivity; Spe, specificity
Next, we checked the accuracy of classifying NL, OC, PB, and PDAC into one of the three risk groups (Table 7). When 0.22 and 0.88 were selected as the threshold combination, the number of samples belonging to the high-, intermediate-, and low-risk groups for NL type was 8, 92, and 83, respectively. On the other hand, the corresponding numbers for PDAC type were 125, 144, and 7. Eight NL samples belonged to the high-risk group and the PDAC samples belonging to the low-risk group were seven. Therefore, we confirmed that our proposed prediction model has good prediction performance for PDAC. These results are demonstrated through the box plot and density plot (Figure 2c–f).
Table 7. Comparison of classified table of type into the predicted low, intermediate, and high risk groups
Group
|
Low
|
Inter
|
High
|
Low
|
Inter
|
High
|
Low
|
Inter
|
High
|
Low
|
Inter
|
High
|
Cut-off
|
|
0
|
|
|
95
|
|
|
94
|
|
|
93
|
|
NL
|
21
|
160
|
2
|
42
|
138
|
3
|
52
|
127
|
4
|
63
|
115
|
5
|
OC
|
27
|
115
|
3
|
41
|
100
|
4
|
50
|
91
|
4
|
59
|
81
|
5
|
PB
|
12
|
302
|
0
|
24
|
286
|
4
|
39
|
271
|
4
|
46
|
259
|
9
|
PDAC
|
0
|
264
|
12
|
1
|
216
|
59
|
2
|
196
|
78
|
3
|
176
|
97
|
Cut-off
|
|
92
|
|
|
91
|
|
|
90
|
|
|
89
|
|
NL
|
72
|
105
|
6
|
81
|
96
|
6
|
83
|
92
|
8
|
96
|
77
|
10
|
OC
|
63
|
74
|
8
|
72
|
65
|
8
|
76
|
60
|
9
|
82
|
53
|
10
|
PB
|
54
|
246
|
14
|
74
|
226
|
14
|
78
|
220
|
16
|
91
|
204
|
19
|
PDAC
|
3
|
159
|
114
|
7
|
155
|
114
|
7
|
144
|
125
|
9
|
138
|
129
|
Cut-off
|
|
88
|
|
|
87
|
|
|
86
|
|
|
85
|
|
NL
|
97
|
75
|
11
|
105
|
65
|
13
|
108
|
59
|
16
|
113
|
54
|
16
|
OC
|
82
|
53
|
10
|
93
|
39
|
13
|
94
|
37
|
14
|
99
|
31
|
15
|
PB
|
93
|
199
|
22
|
100
|
180
|
34
|
105
|
170
|
39
|
109
|
161
|
44
|
PDAC
|
9
|
131
|
136
|
14
|
100
|
162
|
14
|
89
|
173
|
17
|
82
|
177
|
PDAC, pancreatic ductal adenocarcinoma; NL, normal; OC, other cancer; PB, pancreatic benign; Inter, intermediate
Lastly, we compared the mean of the four measures by using test data of each data type (Table 5). The prediction model had been trained on NL and PDAC data, but we intended to check if the model had effective performance in other data categories such as PB and OC. For this purpose, the test data of each type were compared in pairs, such as NL vs. PDAC, OC vs. PDAC, PB vs. PDAC, and non-PDAC (NL, OC, and PB) vs. PDAC. The mean of the four measures was highest at 93.0282 when verified with the test data set of NL and PDAC type combination. In contrast, the mean was the lowest at 89.5232 when PB and PDAC type data were used. In case of non-PDAC vs. PDAC the mean was 89.680, showing a moderate performance between NL vs. PDAC and PB vs. PDAC. This result indicates that PB has intermediate properties between NL and PDAC, as shown in the above table, density plot, and box plot. Based on these results, it was confirmed that OC has characteristics close to NL and that PB does not belong to either NL or PDAC.
Finally, even when different types of data including NL, PDAC, OC, and PB were tested, the proposed prediction model demonstrated satisfactory performance.