3.1 Basic clinical characteristics
The patients’ baseline characteristics are shown in Table 1. A total of 44,907 PCa patients diagnosed with PSA from 2000 to 2014 were identified from the SEER database, with 21,209 patients (47.2%) in the high tumor differentiation group and 23,689 patients (52.8%) in the low tumor differentiation group. The whites accounted for the largest proportion (83.3%). The tumor sizes of 6,296 patients (14%) were less than 50 mm intraoperatively, and 24,617 patients (54.8%) did not receive primary site surgery. The patients with 1–3 lymph nodes resected intraoperatively represented the largest proportion (75.5%); 44,671 patients (99.5%) did not receive chemotherapy; 24,617 patients (54.8%) did not develop lymph node metastasis; it was not the first surgery for only 170 patients (0.4%) to resect distant lymph nodes or other tissues or organs outside the primary site. There were 33,08 patients (7.3%) with a Grade score of ≥ 7. Significant differences were observed between 18,764 (41.8%) patients who received radiotherapy and 26,143 (58.2%) patients who did not receive radiotherapy (p = 0.008).
Table 1
factors | define | Train(N=) | Test(N = 5160) | All(N = 17200) | t/z(p) |
marriage | Married | 24647(78.4) | 10542(78.3) | 35189(78.4) | 0.134(0.717) |
Unmarried | 6788(21.6) | 2930(21.7) | 9718(21.6) |
RACE | White | 26222(83.4) | 11192(83.1) | 37414(83.3) | 0.951(0.622) |
Black | 3873(12.3) | 1704(12.6) | 5577(12.4) |
other | 1340(4.3) | 576(4.3) | 1916(4.3) |
Grade | High_level | 14811(47.1) | 6398(47.5) | 21209(47.2) | 0.532(0.470) |
low_level | 16624(52.9) | 7074(52.5) | 23698(52.8) |
icD | Adenocarcinoma | 30899(98.3) | 13277(98.6) | 44176(98.4) | 3.910(0.052) |
other | 536(1.7) | 195(1.4) | 731(1.6) |
Combine_stage | localized | 26753(85.1) | 11403(84.6) | 38156(85.0) | 1.586(0.210) |
Regional | 4682(14.9) | 2069(15.4) | 6751(15.0) |
Rx_sps | 0 | 17264(54.9) | 7353(54.6) | 24617(54.8) | 0.440(0.508) |
10–90 | 14171(45.1) | 6119(45.4) | 20290(45.2) |
Rx_SRLS | 1to3 | 23793(75.7) | 10123(75.1) | 33916(75.5) | 2.125(0.346) |
≥ 4 | 2808(8.9) | 1205(8.9) | 4013(8.9) |
None | 4834(15.4) | 2144(15.9) | 6978(15.5) |
Rx_soR | None | 31323(99.6) | 13414(99.6) | 44737(99.6) | 1.378(0.241) |
Non_first_ surgery | 112(0.4) | 58(0.4) | 170(0.4) |
Rx_ss | No_radiation | 30286(96.3) | 12992(96.4) | 43278(96.4) | 0.500(0.919) |
after | 1105(3.5) | 46O(3.4) | 1565(3.5) |
before and after | 39(0.1) | 17(0.1) | 56(0.1) |
prior | 5(0.0) | 3(0.0) | 8(0.0) |
Radiation | None | 18296(58.2) | 7847(58.2) | 26143(58.2) | 0.008(0.933) |
Received_radiotherapy | 13139(41.8) | 5625(41.8) | 18764(41.8) |
Chemotherapy | None | 31278(99.5) | 13393(99.4) | 44671(99.5) | 1.364(0.254) |
Yes | 157(0.5) | 79(0.6) | 236(0.5) |
GLEASON | ≤ 6 | 1236(3.9) | 561(4.2) | 1797(4.0) | 4.960(0.084) |
≥ 7 | 2269(7.2) | 1039(7.7) | 3308(7.4) |
unknow | 27930(88.9) | 11872(88.1) | 398o2(88.6) |
Tumor_size | ≤ 5o | 4365(13.9) | 1931(14.3) | 6296(14.0) | 1.919(0.589) |
50–100 | 94(0.3) | 36(0.3) | 130(0.3) |
> 100 | 26(0.1) | 12(0.1) | 38(0.1) |
unknow | 26950(85.7) | 11493(85.3) | 38443(85.6) |
PCa samples (n = 44,907) were randomized into the training set (n = 31,435) and validation set (n = 13,472) at a 7:3 ratio. The training set was used to determine prognostic factors and construct a risk model accordingly. The model was validated in the training and validation sets respectively. The mean age of patients diagnosed with SPMs was 67.18 ± 8.205 years old in the training set and 67.15 ± 8.277 years old in the validation set, respectively. There was no statistical difference in baseline characteristics between the two sets, as shown in Table 1.
3.2 Influencing factors related to poor outcomes of patients with SPMs after PCa
The results of the univariate regression conducted in the training set revealed that age recode with single ages and 100, Race recode, ICD-O-3 Hist/behav, Chemotherapy recode, Radiation recode, Gleason Score Clinical Recode, Grade, CS tumor size, RX Summ - Surg Prim Site, RX Summ - Surg/Rad Seq, RX Summ - Scope Reg LN Sur, and RX Summ - Surg Oth Reg/Dis were associated with the poor prognosis of patients with SPMs after PCa. The CIF curve presented that the cumulative rate of specific mortality in PCa patients rose with the increase in the follow-up time (Fig. 1). The multivariate analysis results revealed that survival-related prognostic variables included age (HR = 1.02, 95% CI = 1.01–1.03), race (with the whites as a reference, the blacks: HR = 1.16, 95% CI = 1.03–1.32; others: HR = 1.03, 95% CI = 0.84–1.26), marital status (with the married as a reference, the unmarried: HR = 1.4, 95% CI = 1.27–1.55), chemotherapy (with the patients who did not receive chemotherapy as a reference, those who received chemotherapy: HR = 2.51, 95% CI = 1.74–3.63), radiotherapy (with the patients who did not receive radiotherapy as a reference, those who received radiotherapy: HR = 0.69, 95% CI = 0.62–0.77), Gleason score (with the patients with the Gleason score of ≤ 6 as a reference, those with the Gleason score of ≥ 7: HR = 3.05, 95% CI = 1.67–5.58), tumor differentiation degree (with the patients with high tumor differentiation degree as a reference, those with low tumor differentiation degree: HR = 1.81, 95% CI = 1.65–2), primary site surgery (with the patients who did not receive PCa-related surgery as a reference, those who received PCa-related surgery: HR = 0.48, 95% CI = 0.41–0.56), number of intraoperatively resected lymph nodes (with the patients in whom the number of intraoperatively resected lymph nodes was 1 to 3 as a reference, those in whom the number was ≥ 4: HR = 1.35, 95% CI = 1.07–1.7), sequence of surgery and radiotherapy (with the patients who did not receive radiotherapy as a reference, those who received postoperative radiotherapy: HR = 2.69, 95% CI = 2.15–3.36; patients who received preoperative and postoperative radiotherapy: HR = 3.93, 95% CI = 1.24–1.26; those who received preoperative radiotherapy: HR = 3.3, 95% CI = 1.34–8.16), and tumor size (with the subjects having a tumor size of ≤ 50 mm as a reference, those with a tumor size of 50 to 100 mm: HR = 2.02, 95% CI = 1.02–4.01; a tumor size of > 100 mm: HR = 1.92, 95% CI = 0.48–7.74). These clinical prognostic variables were all incorporated into a competing risk nomogram model for further analysis (Table 2).
Table 2
Univariate and Multivariate Analyses
| Univariate | Multivariate |
factors | define | HR(95%CD) | Z(P) | HR(95%CI) | Z(P) |
Age | Age | 1.03(1.03–1.04) | 0 | 1.02(1.01–1.03) | |
chemotherapy | YES | 3.32(2.32–4.75) | 0 | 2.51(1.74–3.63) | |
NO | | | | |
Combine_Stage | Localized | | | | |
Regional | 1.38(1.23–1.54) | 0 | 1.73(1.51–1.98) | |
GLEASON | < 6 | | | | |
≥ 7 | 4.51(2.47–8.23) | 0 | 3.05(1.67–5.58) | 3.00E-04 |
unknow | 4.68(2.65–8.25) | 0 | 2.72(1.53–4.83) | 0.0006 |
Grade | High_level | | | | |
low_level | 1.87(1.71–2.05) | | 1.81(1.65-2) | |
ICD | Adenocarcinoma | | | |
other | 1.17(0.87–1.57) | 0.31 | NA | NA |
Marriage | Married | | | | |
Unmarried | 1.53(1.4–1.69) | 0 | 1.4(1.27–1.55) | |
Race | White | | | | |
Black | 1.25(1.11–1.42) | 3.00E-04 | 1.16(1.02–1.32) | 0.02 |
other | 1.14(0.93–1.4) | 0.2 | 1.03(0.84–1.26) | 0.79 |
Radiation | None | | | | |
Received_radio | 1.19(1.09–1.3) | 1.00E-04 | 0.69(0.62–0.77) | |
Rx_SOR | None | | | | |
Non_first_surge] | 1.51(0.81–2.83) | 0.2 | NA | NA |
Rx_SPS | 0 | | | | |
10–90 | 0.59(0.54–0.65) | 0 | 0.48(0.41–0.56) | |
RX_SRLS | 1to3 | | | | |
≥ 4 | 1.45(1.15–1.84) | 0.0017 | 1.35(1.07–1.7) | 0.013 |
None | 1.97(1.61–2.41) | 0 | 1.67(1.33–2.08) | 0 |
Rx_SS | No_radiation | | | | |
after | 1.79(1.49–2.15) | 0 | 2.69(2.15–3.36) | 0 |
before and aftej | 3.02(0.5-18.27) | 0.23 | 3.93(1.24-12.461 | 0.02 |
prior | 1.95(0.79–4.79) | 0.15 | 3.3(1.34–8.16) | 0.0097 |
tumor_size | ≤ 50 | | | | |
50–100 | 2.92(1.52–5.59) | 0.0013 | 2.02(1.02–4.01) | 0.045 |
> 100 | 1.83(0.44–7.58) | 0.4 | 1.92(0.48–7.74) | 0.36 |
unknow | 1.6(1.37–1.87) | 0 | 1.24(1.05–1.46) | 0.011 |
3.3 Construction and validation of the competing risk nomogram for specific survival of patients with SPMs after PCa
Based on the univariate and multivariate analyses, the predictive factors with p < 0.05 were selected to establish a competing risk nomogram model to predict the 3-, 5-, and 10-year specific survival of patients with SPMs after PCa. The following 12 clinical indicators were included in our competing risk model: age recode with single ages and 100, Chemotherapy recode, Radiation recode, Gleason Score Clinical Recode, Race recode, Grade, Marital status at diagnosis, CS tumor size, RX Summ - Surg Prim Site, RX Summ - Surg/Rad Seq, RX Summ - Scope Reg LN Sur, and COMBINED SUMMARY STAGE. In order to assess the discriminative capability of the constructed competing risk model, its accuracy was assessed using the C-index. The C-index values of the nomogram in the training and validation set were 0.70 (se: 0.001) and 0.684 (se: 0.002) respectively, indicating that the model had high discriminative power. ROC curves were plotted to analyze the AUCs in the training and validation set (as shown in the figures below). The AUCs for predicting the three-year, five-year, and ten-year CSS were 0.75 (95% CI: 0.72–0.77), 0.73 (95% CI: 0.72–0.75), and 0.72 (95% CI: 0.7–0.73) in the training set, and 0.7 (95% CI: 0.65–0.74), 0.7 (95% CI: 0.67–0.73), and 0.71 (95% CI: 0.69–0.73) in the validation set, respectively. The model’s prediction fits the actual observation well, as the calibration curve indicates (Fig. 2).
3.5 Comparison of mortality estimation between traditional survival analysis and competing risk model
As shown in the figure below, the 3-, 5-, and 10-year mortality risks estimated through traditional survival analysis were 2.37%, 4.41%, and 10.43% respectively, while the cumulative specific mortality risks predicted by the competing model were 1.34%, 2.49%, and 5.75% respectively. The results showed a big difference in the mortalities estimated by traditional survival analysis and the competing risk model. In this study, the mortality estimated through the conventional method was higher than that predicted by the competing model. Since the PCa patients who died from other causes accounted for a relatively large proportion in this study, the specific mortality of PCa patients may be overestimated in traditional COX regression analysis (Supplementary Table 1).