Cancer of unknown primary (CUP): A population-based analysis of temporal change and socioeconomic disparities.

Abstract

e17535 Background: CUP is the 4th most common cause of cancer death. With advanced diagnostic investigations and treatment of cancer, we hypothesized that the proportion of cancers diagnosed as CUP and survival outcomes of CUP have changed and examination of these changes may identify socioeconomic disparities in the US. Methods: We analysed trends in CUP diagnosis and outcome within the SEER registry between 1973-2008. The relationship between demographic and tumour characteristics with survival was investigated. Results: The incidence and percentage of all cancers diagnosed as CUP have decreased over time (incidence 8.9 vs 6.2 per 100,000 and percentage 3.9% vs 1.9% of all cancer diagnoses in 1973 vs 2008 respectively). Significantly more females were labelled as CUP without a pathological confirmation (25% vs 20% in males, p<0.001). A higher proportion of CUP was diagnosed in females, blacks and residents of less affluent or less educated counties. The 5 year survival significantly improved in those with squamous histology (SqC) but only marginally in those with non-SqC CUP. The improvement in survival over time within SqCC was more pronounced among some socioeconomic groups (SEG; Table). For the entire cohort, factors associated with a longer survival on multivariate analysis included: white race; female; <65 years old; most recent decade at diagnosis; grade 1; SqC; married; a histologic diagnosis and treatment with radiotherapy (all p<0.001). Despite the improvement in survival with radiotherapy (RT), the use of RT was less frequent in females and blacks. Conclusions: The percentage of cancers diagnosed as CUP is decreasing but prognosis remains poor, particularly in non-SqCC CUP. However, significant disparities in the diagnosis and survival between SEG exist, suggesting inequalities in access to diagnostic investigations and treatment. [Table: see text]