Basic characteristics of the patients
The basic demographic characteristics of all the patients in this study were shown in table 1. The majority of the patients were married and Caucasians. 55.17% of target population were over 65 years old and about 50.68% were males. Most of the patients (64.56%) had tumor lesions in the head of the pancreas. Moderately differentiated tumors (41.26%) constituted the majority of the population. Among the 21,030 patients, most of them were stage T2, accounting for 50.87% (10699 patients), and about 4.60% (968 patients) were stage T4. In terms of treatment regimen, about 42.33% of patients only were managed with surgical treatment, about 30.37% received surgery plus chemotherapy, about 23.61% received postoperative adjuvant radiotherapy, and only about 3.69% underwent neoadjuvant radiotherapy.
Survival Analysis Before Propensity Score Matching
Using univariate and multivariate Cox proportional risk analysis for the total population(Table 2), uninsured status, single status, advanced age (≥65 years old), pancreatic head tumor, high tumor grade, tumor T, N stage, therapy methods and regional nodes examined <15 were all relevant to poor prognosis (all P <0.001). The Kaplan Meier curve of overall survival in PDAC patients were shown in Figure 2. For patients with non-metastatic PDAC, neoadjuvant radiotherapy, adjuvant radiotherapy and surgery plus chemotherapy had significantly better OS than surgery alone (P < 0.001). After adjusting for insurance status, marital status, age, race, gender, tumor site, tumor grade, T stage, N stage and regional nodes examined, multivariate Cox analysis of different treatment methods was performed, and the influence of each group on OS was shown in table 3. The mean 1-, 3-year survival rates for PDAC patients were shown in table 4.
The OS of surgery plus chemotherapy (HRs =0.896, 95%CIs, 0.827-0.970; P=0.007) were significantly better than the other three treatments in stage T1-3N0M0 PDAC patients. Adjuvant radiotherapy (HRs=0.950; 95% CIs, 0.874-1.032; P=0.223), and only surgery had similar OS results. However, neoadjuvant radiotherapy (HRs = 1.171;95% CIs, 1.019-1.347; P=0.027) seems to be a risk factor for OS. The median survival for only surgery, surgery plus chemotherapy, neoadjuvant radiotherapy and adjuvant radiotherapy was 21moths, 25moths, 19moths, 24moths, respectively. Adjuvant radiotherapy (HRs=0.613, 95% CIs, 0.579-0.649; P< 0.001) had significantly better OS results than surgery plus chemotherapy (HRs=0.686; 95% CIs, 0.649-0.726;P < 0.001) and neoadjuvant radiotherapy (HRs=0.751; 95% CIs, 0.635-0.887; P=0.001) in stage T1-3N+M0 patients, with median survival of 19 moths, 15 moths, and 16 moths, respectively. Specially, for stage T4N0M0 patients, neoadjuvant radiotherapy (HRs=0.482, 95% CIs, 0.347-0.670; P < 0.001) had significantly better OS outcomes than surgery plus chemotherapy (HRs=0.588; 95% CIs, 0.424-0.814; P=0.001) and adjuvant radiotherapy (HRs=0.858; 95% CIs, 0.621-1.185; P=0.353), with median survival of 20 moths, 17 moths, and 14 moths, respectively. Similarly, for stage T4N+M0 patients, neoadjuvant radiotherapy (HRs=0.338, 95% CIs, 0.215-0.532; P < 0.001) had significantly longer OS outcomes than adjuvant radiotherapy (HRs=0.430; 95% CIs, 0.334-0.554; P < 0.001) and surgery plus chemotherapy (HRs=0.530; 95% CIs, 0.411-0.683; P < 0.001), with median survival of 17 moths, 16 moths, and 10 moths, respectively.
Survival Analysis After Propensity Score Matching
The balanced population of the neoadjuvant radiotherapy group and the only surgery group(n=296), the neoadjuvant radiotherapy group and the adjuvant radiotherapy group(n=208), the neoadjuvant radiotherapy group and the surgery plus chemotherapy group(n=288) were obtained by multiple 1:1 propensity score matching for stage T1-3N0M0 PDAC patients. Before and after the PSM, the results of univariate and multivariate analyses of OS in different groups were shown in table 5. The OS of the neoadjuvant radiotherapy group was no better than that of the adjuvant radiotherapy group(HRs=0.807; 95% CIs, 0.649-1.035; P =0.125) and the only surgery group(HRs=1.164; 95% CIs, 0.934-1.449; P =0.176), while the OS of the surgery plus chemotherapy group was better than that of the neoadjuvant radiotherapy group(HRs=1.280; 95% CIs, 1.045-1.574; P =0.025) in stage T1-3N0M0 PDAC patients.
Similarly, the 1:1 propensity score matching was used to obtain the balanced population of the neoadjuvant radiotherapy group and the only surgery group(n=155), neoadjuvant radiotherapy group and the adjuvant radiotherapy group (n=153), neoadjuvant radiotherapy group and the surgery plus chemotherapy group (n=166) in stage T1-3N+M0 PDAC patients. The OS of the neoadjuvant radiotherapy group was better than that of the only surgery group (HRs=0.618; 95% CIs, 0.429-0.863; P =0.036), but there was no difference with that of the operation plus chemotherapy group (HRs=1.083; 95% CIs, 0.838-1.400; P =0.541). The adjuvant radiotherapy group had the best prognosis (HRs=1.364; 95% CIs, 1.046-1.777; P =0.022).
The 1:1 propensity score matching was used to obtain the balanced population of the neoadjuvant radiotherapy group and the only surgery group(n=104), neoadjuvant radiotherapy group and the adjuvant radiotherapy group (n=102), neoadjuvant radiotherapy group and the surgery plus chemotherapy group (n=138) in stage T4 PDAC patients. The OS of neoadjuvant radiotherapy group was better than that of only surgery group (HRs=0.466; 95% CIs, 0.331-0.657; P <0.001), adjuvant radiotherapy group (HRs=0.589; 95% CIs, 0.419-0.830; P =0.002) and surgery plus chemotherapy group (HRs=0.707; 95% CIs, 0.519-0.963; P =0.028). The Kaplan-Meier curve of overall survival of PDAC patients after PSM were shown in figure 3.