1. Patient information
As of January 1, 2022 (end time of follow-up), 71 patients with gastric cancer were included (Table 1).
2. Prognosis by clinicopathological features and PET/CT metabolic parameters
2.1 Overall prognosis
The mean follow-up time for the 71 patients was 28 months, with a total follow-up time of 5–69 months. During the follow-up period, disease progression occurred in 27 (38.0%) patients, including 23 (32.4%) males and four (5.6%) females, and 24 (33.8%) patients died, including 18 (25.4%) males and six (8.5%) females. Mean PFS was 25 months, and the cumulative PFS rates at 1, 2, and 3 years were 76.1%, 67.6%, and 64.8%, respectively. The mean OS was 28 months, and the cumulative OS rates at 1, 2, and 3 years were 83.1%, 73.2%, and 69.0%, respectively.
2.2 Intergroup comparison in patients with different prognosis
Among the clinicopathological factors, the minimum tumor diameter, carcinoembryonic antigen (CEA), and Carbohydrate antigen 12-5(CA12-5) were 6.20 (3.15, 7.40) cm, 5.78 (2.60, 8.58) ng/ml, and 31.73 (21.10, 39.81) U/ml, respectively, which were significantly higher than those in patients without disease progression, at 2.05 (1.18, 3.28) cm, and 2.13 (1.03, 3.57) ng/ml, and 9.87 (6.69, 13.83) U/ml, respectively, with statistically significant differences (all P < 0.05). In PET/CT metabolic parameters and heterogeneity index, MTV, TLG, and HI-1 were 28.69 (14.27, 41.71) cm3, 156.13 (49.28, 253.02) g, and 6.47 (4.62, 10.00), respectively, in patients with disease progression, which were significantly higher than those without disease progression, 8.15 (5.55, 17.26 ) cm3, 34.26 (15.94, 76.45) g, and 2.53 (1.50, 3.65), respectively, with statistically significant differences (all P < 0.05). No other factors significantly correlated with patient prognosis (Table 2).
2.3 Cox regression analysis for PFS
Tumor minimum diameter, CA12-5, MTV, TLG, and HI-1 were significantly associated with PFS in gastric cancer patients (all P < 0.05). Multivariate Cox regression analysis showed that tumor minimum diameter (HR: 1.192, 95% CI: 1.025–1.387, P = 0.023), CA12-5 (HR: 1.028, 95% CI: 1.009–1.048, P = 0.003), and HI-1 (HR: 1.183, 95% CI: 1.010–1.387, P = 0.037) were independent risk factors for PFS in patients with gastric cancer (Table 3).
2.4 Cox regression analysis for OS
Univariate Cox regression analysis showed that MTV, TLG, and HI-1 were significantly associated with OS (all P < 0.05). Multivariate Cox regression analysis showed that HI-1 (HR: 1.214, 95% CI: 1.016–1.450, P = 0.032) was an independent risk factor for OS in patients with gastric cancer (Table 4).
3. Construction of the nomogram
3.1 PFS
The nomogram to predict PFS was constructed based on the results of the Cox multivariate regression analysis (Fig. 1). Probabilistic calibration curves for 1-, 2-, and 3-year PFS showed good agreement between the nomogram-predicted PFS and the actual results (Fig. 2). The AUCs at 1, 2, and 3 years were 0.845 (95% CI: 0.749–0.942), 0.869 (95% CI: 0.768–0.970), and 0.894 (95% CI: 0.785–1.000), respectively (Fig. 3). The nomogram was constructed using DCA to allow for a greater net clinical benefit to the patients (Fig. 4).
3.2 OS
The nomogram to predict OS was constructed based on the results of the Cox multivariate regression analysis (Fig. 5). Probabilistic calibration curves for 1-, 2-, and 3-year OS showed good agreement between the nomogram-predicted OS and the actual results (Fig. 6). The AUCs at 1, 2, and 3 years were 0.731 (95% CI: 0.530–0.931), 0.738 (95% CI: 0.583–0.892), and 0.739 (95% CI: 0.585–0.893), respectively (Fig. 7). The nomogram was constructed using DCA to allow for a greater net clinical benefit to the patients (Fig. 8).
4. Risk stratification and Kaplan–Meier survival analysis
With disease progression as a positive event, ROC curves were plotted for independent risk factors (tumor minimum diameter, CA12-5, and HI-1) for PFS in gastric cancer patients, and the optimal thresholds were calculated by the Youden index. The optimal thresholds for the three factors were 3.60 cm, 17.15 U/ml, and 3.80, respectively, and the patients were divided into low, medium, and high-risk groups, accordingly. Those with a tumor minimum diameter < 3.60 cm, CA12-5 < 17.15 U/ml, and HI-1 < 3.80 were entered into the low-risk group, totaling 23 (32.4%) cases; those with the tumor minimum diameter ≥ 3.60 cm, CA12-5 ≥ 17.15 U/ml, and HI-1 ≥ 3.80 were entered into the high-risk group, totaling 15 (21.1%) cases; the remaining patients were entered into the intermediate-risk group, totaling 33 (46.5%) cases. Kaplan–Meier survival analysis was used to compare the PFS of patients among the three groups, and the results showed a statistically significant difference (P < 0.05). After Bonferroni correction of P values for two-way comparisons between groups, the results showed statistically significant differences between all groups (all P < 0.017) (Fig. 9).
With death as a positive event, ROC curves were plotted for independent risk factors (HI-1) for OS in patients with gastric cancer, and the results showed that the optimal threshold for HI-1 was 6.12. Patients were divided into low-risk (HI-1 < 6.12) and high-risk (HI-1 ≥ 6.12) groups according to the threshold. The results showed that the number of patients in the low- and high-risk groups was 52 (73.2%) and 19 (26.8%), respectively. Kaplan–Meier survival analysis showed a statistically significant difference in OS between patients in the low- and high-risk groups (P < 0.05) (Fig. 10).