Incidence and Outcomes of Metastatic Patterns of Pancreatic Ductal Adenocarcinoma

Introduction Pancreatic ductal adenocarcinoma (PDAC) is considered one of the most aggressive malignancies, with approximately 90% of patients presenting with advanced disease. Despite advances in the treatment therapies over the last 30 years, the 5-year survival rate for Stage IV disease is approximately 3%. Understanding patterns of metastatic burden may refine staging and guide treatment goals and outcomes. This study evaluates metastatic distribution and site-specific survival among patients with PDAC using a large, recent nationwide cohort. Methods Data on all patients with metastatic PDAC were abstracted from the Nationwide Inpatient Sample (NIS) database (1998-2018). Patterns of metastases were identified using ICD-9 codes. Sites and rates of metastatic patterns were recorded. Standard statistical methods were used, and binary logistic regression was performed to assess the influence of metastatic site(s) on mortality. Results In total, 119,620 patients were analyzed with a diagnosis of metastatic PDAC. The most common sites of metastases included liver (31%), regional abdominal lymph nodes (10%), peritoneum (8.5%), and respiratory tract (6%). The small intestine (4.1%) was more frequently involved than the large intestine (0.9%). The least common nodal site was the axillary nodes (0.05%). Less than 1% of patients had metastases in the head/neck and pelvic lymph nodes (0.2%), thoracic and mediastinal nodes (0.5%), or inguinal nodes (0.5%). Bone metastases (2.4%) were more common than ovarian (0.2%), renal (0.3%), and adrenal (0.7%) metastases. Brain metastases occurred in 0.4% of patients, and skin (0.1%) and CNS not otherwise classified (0.1%) were rarely involved. Metastases to lung (OR = 1.5), liver (OR = 1.7), brain and spinal cord (OR = 1.8), and bone (OR = 1.3), and presence of malignant ascites (OR = 2.03) independently influenced mortality, P = 0.01. Conclusion Based on NIS data, PDAC predominantly metastasizes to the liver, regional nodes, peritoneum, lung, and small intestine. Metastases to atypical sites are rare and suggest advanced burden of disease. Mortality was independently influenced by metastases to lung, liver, brain and spinal cord, bone, and peritoneum. Increased knowledge of metastatic patterns and site-specific survival may help guide decision-making regarding the treatment plan in terms of palliative care or adjuvant therapy.