Patient baseline statistics
A total of 5861 cases with gallbladder cancer were enrolled, including 5622 (95.9%) patients without prior primary cancer and 239 (4.1%) patients with prior primary cancer. Table 1 shows the comparison of baseline statistics between the two groups. Patients with gallbladder cancer with prior primary cancer were older, with a greater proportion of people aged ≥ 65 years (76.6% VS 64.0%, P<0.001). The tumors were more localized and regional according to the SEER stage, and the AJCC(American Joint Committee on Cancer) stage was at more early stages. In terms of treatment, gallbladder cancer patients with prior primary cancer received less chemotherapy (29.3% VS 36.2%, P=0.028).
Fig. 1 shows the SEER stage and AJCC stage of the gallbladder cancer patients with and without prior primary cancer. Fig. a and Fig. b show the SEER stages of the patients with gallbladder cancer with and without prior primary cancer. Localized, regional, and distant stages accounted for 16.7%, 59.8%, and 23.4% and 11.6%, 53.0%, and 35.4%, respectively. Fig. c and Fig. d shows the AJCC stages of patients with gallbladder cancer with and without prior primary cancer. AJCC stages I, II, III, and IV accounted for 44.8%, 33.1%, 1.7%, and 20.5% and 32.6%, 34.3%, 2.7%, and 30.4%, respectively.
Prior primary cancer and interval time
As Table 2 shows, among those with prior primary cancer, 59 had gastrointestinal cancer, 51 had prostate cancer, 49 had breast cancer, 42 had urogenital cancer, 11 had lung cancer, and 27 had other types of cancer. The median time from the prior prostate malignancy diagnosis to the subsequent diagnosis of gallbladder cancer was the longest (45.04 months), while the median time from the prior gastrointestinal malignancy diagnosis to the subsequent diagnosis of gallbladder cancer was the shortest (21.47 months), with the rest ranging from 25.00 to 37.80 months (Fig. 2).
Comparison of mortality in gallbladder cancer patientswith and without prior cancer
The 1-year overall mortality and 5-year overall mortality of gallbladder cancer individuals without prior primary cancer was 64.6% and 97.1%, respectively, and 58.0% and 95.5%, respectively, of gallbladder cancer individuals with previous malignancy. The gallbladder cancer individuals without previous primary malignancy had higher 1-year overall mortality and 5-year overall mortality.
The 1-year OM of gallbladder cancer individuals with previous primary lung malignancy was the highest (77.8%), while the 1-year OM of gallbladder cancer individuals with previous gastrointestinal malignancy was the lowest(46.3%). The gallbladder cancer individuals with previous lung malignancy and genitourinary malignancy had the highest 5-year OM (100%), while the individuals with gallbladder cancer with previous gastrointestinal malignancy had the lowest 5-year OM (87.8%) (Table 3).
Propensity Score Matching (PSM)
Table 4 shows the results of 1:1 PSM for patients with gallbladder cancer with and without prior primary caner. After PSM, the characteristics were no longer significantly different.
Comparison of OS and GCSS in gallbladder cancerindividuals with and without previous malignancy
The Kaplan-Meier curves showed that gallbladder cancer individuals with prior cancer had greater OS than those without prior cancer (P=0.027, Fig. a) before PSM, although the Kaplan-Meier curves had a cross after 100 months. Individuals with gallbladder cancer with previous malignancy also had a greater GCSS (P<0.001, Fig. b) before PSM.
After PSM, the OS and GCSS of the two groups were compared again. The Kaplan-Meier curves showed that there were no significant differences in OS between patients with gallbladder cancer with and without prior cancer (P=0.113, Fig. c), and patients with gallbladder cancer with prior cancer also had a greater GCSS (P<0.001, Fig. d).
Multivariate analyses of OS and GCSS
To analyze the risk factors of OS and GCSS of the second primary gallbladder cancer, we also conducted a multivariable Cox regression analysis. After incorporating various variables into the model, it was found that the prior history of cancer did not affect OS (HR=0.875, 95%CI: 0.752-1.108, P=0.084). A history of cancer before gallbladder cancer was a protective factor with regard to GCSS (HR=0.404, 95%CI: 0.318-0.513, P<0.001) (Table 5).
Subgroup analysis stratified by types of prior cancer
To explore the effects of prior different cancers on the OS and GCSS of patients with gallbladder cancer, we also conducted a subgroup analysis: prior gastrointestinal cancer was a favorable factor for OS (HR=0.675, 95%CI: 0.496-0.918, P=0.012) and GCSS (HR=0.158, 95%CI: 0.079-0.316, P<0.001); prior prostate cancer was a favorable factor for GCSS (HR=0.486, 95%CI: 0.301-0.785, P=0.003); prior breast cancer was a favorable factor for GCSS (HR=0.579, 95%CI: 0.376-0.889, P=0.013); prior genitourinary cancer was a favorable factor for GCSS (HR=0.579, 95%CI: 0.376-0.889, P=0.013); and prior lung cancer was a adverse factor for overall survival (HR=2.248, 95%CI: 1.167-4.331, P=0.015) (Table 6).