Cancer of unknown primary site: A population-based analysis of demographics and all-cause mortality.

Abstract

e18518 Background: Cancer of unknown primary site (CUP) is an entity that is defined by the presence of an occult primary site despite sufficient workup. Prior analyses have concluded that CUP has a poor overall prognosis. This study aims to examine a recent US cohort of patients with CUP, with a focus on discerning demographic characteristics and common causes of mortality. Methods: Patients with CUP were identified from the Surveillance, Epidemiology, and End Results (SEER) database, a large US population-based cancer registry (using SEER*Stat 8.3.4 software). Patients of all ages with cancers diagnosed between 2010-2014 were included in the study. Patients with CUP were identified by ICD-O-3 code C80.9 (‘Unknown Primary Site’). Data were extracted for adenocarcinomas and squamous cell carcinomas separately. Ill-defined and rarer histologies like ‘carcinoma, NOS’ and neuroendocrine tumors were excluded from this study. Results: The number of cases identified was 9,683 adenocarcinomas and 3,758 squamous cell carcinomas, totaling 13,441 cases that met eligibility. The median age at diagnosis was 71 +/- 13.0 years. Sex distribution was nearly equal, with males accounting for 50.8% of cases, and females 49.2%. Most patients were of ‘White’ race (81.6%), and the remainder comprised ‘Black’ (10.8%), ‘Other’ (American Indian, AK Native, Asian/Pacific Islander) (6.7%), and ‘Unknown’ (0.9%). Adenocarcinoma and its subtypes were the most common histological type reported (71.7%). Notable solid organ metastatic sites irrespective of tumor histology were bone (3.0%), brain (0.6%), liver (5.1%), and lung (0.9%). The median survival of the overall population was 2.0 months. 3,195 patients were alive at the end of the study period. Death from any cancer unsurprisingly accounted for the vast majority of mortality (87.0%). Most non-cancer deaths were caused by cardiovascular disease (4.6%) and infections (1.2%). Conclusions: CUP remains a disease with dismal prognosis. Our study characterizes the demographics and most common causes of death in patients with CUP. Patients who were diagnosed with CUP tended to be elderly, White individuals of either sex. Most patients with CUP died from their cancer, with a median survival duration of two months. Further research is required to evaluate newer treatment modalities such as targeted therapy and immunotherapy in order to improve patient outcomes.