Abstract
Cancer of unknown primary (CUP) and pancreatic cancer (PC) are malignancies associated with poor prognosis. CUP is the fourth most common cause of cancer mortality in the US, and median survival time is 3-4 months. PC is the third most common cause of cancer mortality in the US, and median survival time for patients with stage 3 or 4 PC is 2-3 months. The present study aimed to understand the patient characteristics of those initially misdiagnosed with CUP who ultimately received a diagnosis of PC. The present study used 2010-2015 Surveillance, Epidemiology, and End Results-Medicare data, a US population-based cancer registry linked to Medicare health insurance claims. Odds ratios (ORs) and 95% confidence intervals were calculated using two binary logistic regression models to compare the characteristics of patients who received definitive diagnosis between the CUP-PC group (those with an initial diagnosis of CUP who eventually received a stage 3 or 4 PC diagnosis) and the PC group (those diagnosed with stage 3 or 4 PC only). Approximately 26% of patients who received a definitive diagnosis of metastatic PC started with an initial diagnosis of CUP (n=17,565). The odds of definitive PC diagnosis in patients with CUP were lower for those with a comorbidity score of 0 [OR, 0.85 (95% CI: 0.79, 0.91)] and epithelial/unspecified histology [OR, 0.76 (95% CI: 0.71, 0.82)]. The odds of definitive PC diagnosis in patients with CUP were higher for patients of other race [OR, 1.27 (95% CI: 1.13, 1.43)] compared with white patients. Definitive diagnosis of PC in patients with CUP was lower in patients who were older with fewer or no comorbidities and unspecified histology. The complexity of CUP diagnosis and patient performance status may influence delays in diagnosis to a known primary site.