Increased risk of multiple metastases and worse overall survival of metastatic pancreatic body and tail cancer: a retrospective cohort study.

Background: Pancreatic cancer (PC) is a lethal disease, especially metastatic PC. And it can be divided into two types: head pancreatic cancer (H-PC) and body and tail pancreatic cancer (BT-PC). Prior studies have proved that they have different overall survival (OS) and should be regarded as two different categories of PC. At present, there remains a gap in the field regarding OS across different primary tumor locations and metastatic sites, as well as the metastatic patterns associated with various primary tumor locations in patients with metastatic PC. Thus, our study aims to address this gap by analyzing data from a large population sourced from the Surveillance, Epidemiology, and End Results (SEER) database. The different prognosis of different primary tumor locations and metastatic sites may indicate that different primary locations and metastatic sites may require different therapy and follow-up strategy. It is hoped that these findings will lay the groundwork for future guideline updates and related research. Methods: Patients with pathologically confirmed stage IV metastatic PC from the National Cancer Institute's SEER program between 2010 and 2015 were included, excluding patients with various tumors, without specifying age, specific sites of metastasis, or OS. Data including age, race, gender, tumor size, T stage, N stage, grade, sites, number of metastatic sites, surgery, radiotherapy, chemotherapy and years of diagnoses were collected from the SEER database. OS was defined as the period from initial diagnosis to the date of death. Specific metastatic sites for the different primary locations of tumor were compared. Survival was analyzed by Cox regression analyses. Results: Overall, 14,406 patients with metastatic PC were included in this research (7,104 of H-PC and 7,302 of BT-PC). Gender proportion, tumor size, T stage, N stage, number of metastatic sites surgery of the primary lesions and radiotherapy were different between BT-PC and H-PC. The proportion of only 1 metastatic site was 68.3% in H-PC compared with 58.3% in the BT-PC. The BT-PC was an independent risk factor for liver metastases compared with the H-PC [odds ratio (OR) =1.510; 95% confidence interval (CI): 1.320-1.727]. No matter for those with multiple metastases, or for those with solitary liver or lung metastases, patients with metastatic H-PC showed better OS (P<0.001, P=0.001, P=0.04, respectively). In patients with solitary liver metastases, worse OS was observed in the BT-PC than the H-PC [hazard ratio (HR) =1.109; 95% CI: 1.046-1.175]. Conclusions: The metastatic BT-PC had worse OS and increased risk to suffer from liver and multiple metastases. Moreover, in patients with solitary metastases, those with liver metastases presented poorest survival.