Epidemiology

Adenocarcinoma of unknown primary site (AUP) is a histologic subtype making up approximately 50% to 80% of all cancers of unknown primary site (CUP).[3][4][5][6]​​​​​​​ According to the American Cancer Society, approximately 32,950 new cases of CUP will be diagnosed in the US in 2023, representing about 2% of all new cancer cases.[7]

Incidence increases with age.[8][9]​​​​​ In the UK, between 2016 and 2018, approximately 60% of new cases were diagnosed in people ages 75 years or more.[9] In a US population-based cohort of patients with CUP diagnosed between 2010 and 2014, median age at diagnosis was 71 years.[8] Among the US cohort of 13,441 patients (9683 of whom had adenocarcinoma), most were white (81.6%). The remainder comprised black patients (10.8%); American Indian, Alaska native, Asian/Pacific Islander (6.7%); and unknown race (0.9%).[8] Earlier US analyses reported a higher proportion of CUP among patients who were female or black, or who were living in poverty.[10]​ UK data indicate that CUP incidence rates are lower in women than in men.[9]

An age-standardized annual CUP incidence rate of 14 per 100,000 population (2016-2018) has been reported in the UK.[11]​ Overall, the epidemiologic data relating to CUP are consistent worldwide, likely reflecting the lack of defined risk factors, either genetic or environmental, thus far observed in this entity.

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