Survival and prognostic factors for postoperative primary appendiceal cancer: a retrospective cohort study based on the Surveillance, Epidemiology, and End Results database.

Background: The factors affecting the postoperative survival of patients with primary appendiceal cancer (PAC) have yet to be fully explored. And there are no clear guidelines for adjuvant treatment after appendectomy. Whether chemotherapy can prolong patient survival after appendectomy, is critical in guiding postoperative medications. The majority of studies on appendiceal cancer are single case reports, and they focused on the incidence of appendiceal cancer. The present study aimed to investigate the survival characteristics of patients with primary appendiceal cancer after surgery using the Surveillance, Epidemiology, and End Results (SEER) database. Methods: The data of 2,891 cases of primary appendiceal cancer between 2004 to 2015 were obtained from the SEER database and subjected to survival analysis using the Kaplan-Meier method and Cox proportional-hazards model. The annual percentage change (APC) was calculated using the weighted least squares method. Results: The overall age-adjusted incidence rate per 100,000 population steadily increased from 0.58 in 2004 to 1.63 in 2015. For patients who received chemotherapy, the median overall survival (OS) was 65 months and the 5-year OS rate was 51.9%, and for patients who did not receive chemotherapy or whose chemotherapy status was unknown, the median OS was not reached and the 5-year OS rate was 78.9%. Age [35< age <69: hazard radio (HR) =2.147; 95% confidence interval (CI): 1.442-3.197, P<0.001; age >69: HR =5.259; 95% CI: 3.485-7.937, P<0.001], race (White race: HR =0.728; 95% CI: 0.590-0.899, P=0.003), histologic type (mucinous neoplasm: HR =0.690; 95% CI: 0.580-0.821, P<0.001; malignant carcinoid: HR =0.657; 95% CI: 0.536-0.806, P<0.001), grade (II: HR =1.794; 95% CI: 1.471-2.187, P<0.001; III: HR =2.905; 95% CI: 2.318-3.640, P<0.001; IV: HR =3.128; 95% CI: 2.159-4.533, P<0.001), and stage (localized: HR =0.236; 95% CI: 0.194-0.287, P<0.001; regional: HR =0.425; 95% CI: 0.362-0.499, P<0.001) were identified as independent predictors of survival. And after adjusting for known factors (age, sex, race, tumor size, marital status, histologic type, grade, stage), chemotherapy (HR =1.220; 95% CI: 1.050-1.417, P=0.009) was revealed to be an independent indicator of poor prognosis. Conclusions: There was an increasing trend in the incidence of appendiceal cancer in the United States between 2004 and 2015. Chemotherapy was revealed to be an independent indicator of poor prognosis, which provide valuable insight into the therapy of primary appendiceal cancer. Large clinical trials of chemotherapy and targeted therapy for appendiceal cancer are urgently needed.