Participant characteristics
In a study with 284 patients, 131 experienced disease recurrence and 121 died. Of all patients, 134 (47.2%) were women, while 56 (42.7%) of those who experienced relapse were women and 71 (58.7%) of those who died were men. Patients were categorized based on their age at the time of diagnosis into three groups: less than 50 years, 51 to 70 years, and more than 70 years. The largest group was the second category, with 158 (55.6%) patients, of whom 65 (53.7%) died and 72 (55.0%) had disease recurrence. The majority of patients (85.6%) underwent chemotherapy, of whom 119 (90.8%) relapsed and 109 (90.1%) died. Those who did not undergo chemotherapy were 41 (14.4%), of whom 12 (9.2%) relapsed and 12 (9.9%) died.
The number of chemotherapy sessions was categorized into 3 categories: zero, less than 6 sessions and more than 6 sessions. There were 148 (52.1%) people who had more than 6 sessions of chemotherapy, of which 76 (58.0%) recurrence and 61 (50.4%) died. Body mass index was also categorized into 3 categories: normal, overweight and obese, the patients who were overweight were 180 (63.4%) people, of which 72 (59.5%) died and 80 (61.1%) of them had relapses. Also, among the categorical variables, the stage of the disease variable was also divided into 3 categories B, C and D, the largest number of which was 133 (46.8%) in category B, of which 23 (19.0%) died and 28 (21.4%) had relapses.
Out of the 284 patients, 173 did not have recurrence, but 27 (22.3%) died and 21 (16.0%) experienced recurrence and 111 had recurrence, of which 110 (84.0%) had recurrence and 94 (77.7%) of patients died. We computed the median survival time to be 61.0 months (95% CI: 42.2 - 79.8) and also calculated 1-, 3-, and 5-year survival probabilities with their 95% CI, which were 86.9%, 62.1%, and 50.4%, respectively.
Log - rank tests results
The log-rank test and Kaplan-Meier curve analysis revealed a significant difference in both death and recurrence rates between patient groups (P < 0.001). Patients who received less than 6 chemotherapy treatments had a higher incidence of events compared to those who had no chemotherapy, but the event rate decreased with more than 6 chemotherapy sessions (P < 0.05). The rate of non-terminal and terminal events increased significantly with an increase in the level of disease stage and PT stage (P < 0.001), as shown in Figures 1-3.
To determine the optimal model, several distributions were evaluated, and the selection was based on Akaike information criterion (AIC) and Bayesian information criterion (BIC). A lower value for these criteria indicates a better model fit. After comparing the different models, the Log-logistic model was selected as the best fit, and the results from this model are presented in Table 1.
Table 1 : Model comparison
|
|
AIC
|
BIC
|
Log logistic
|
6821.698
|
6967.657
|
Log normal
|
68.25.421
|
6971.380
|
Weibull
|
6861.593
|
7007.552
|
Exponential
|
6956.292
|
7094.953
|
Predictors of time recurrence:
Here are the time ratios (TR) and 95% confidence intervals (CI) for the disease stage in each of the 4 fitted models:
- Weibull survival model: TR = 0.394, CI95%: (0.315, 0.492)
- Exponential survival model: TR = 0.393, CI95%: (0.318, 0.485)
- Log-normal survival model: TR = 0.429, CI95%: (0.341, 0.540)
- Log-logistic model: TR = 0.433, CI95%: (0.348, 0.539)
In each model, the time ratio represents the change in the recurrence time associated with a one-unit increase in the disease stage. For example, in the Weibull survival model, a one-unit increase in disease stage is associated with a 0.394-fold decrease (or 60.6% decrease) in the recurrence time, with a 95% confidence interval ranging from 0.315 to 0.492.
In figures 4 to 7, powerful graphical representations of the conceptual models for Weibull, Log-normal, Exponential, and Log-logistic survival models have been demonstrated.
Result for Log-logistic model
Based on the results of the optimal model, the increase in the recurrence time was related to the increase in the survival time [TR=1.020, confidence interval 95% (CI):1.018 - 1.022], Also, participating in chemotherapy sessions decreased the survival time [TR=0.443, 0.307 - 0.637], but increasing the number of chemotherapy sessions to more than 6 sessions increased the survival time [TR=2.007, 1.690 - 2.383].
In this model, the disease recurrence time is related to the recurrence variable chemotherapy. Participating in chemotherapy sessions decreased the recurrence time [TR=0.290, 0.146 - 0.576], but increasing the number of chemotherapy sessions to more than 6 sessions increased the recurrence time [TR=2.351, 1.710 - 3.232]. The time ratio of disease stage was [TR=0.433, 0.348- 0.539] therefore, disease stages were associated with a decrease of approximately 0.57 recurrence time. The ratio of recurrence time of variable age_cat2 was equal to [TR=0.753, 0.597- 0.949] (Figure 7).