Health-related predictors of cancer registry-notified cancer of unknown primary site (CUP).

BACKGROUND: The relationship between comorbid disease and health service use and risk of cancer of unknown primary site (CUP) is uncertain. METHODS: A prospective cohort of 266,724 people aged 45 years and over in New South Wales, Australia. Baseline questionnaire data were linked to cancer registration, health service records 4-27 months prior to diagnosis, and mortality data. We compared individuals with incident registry-notified CUP (n = 327; 90% C80) to two sets of randomly selected controls (3:1): (i) incident metastatic cancer of known primary site (n = 977) and (ii) general cohort population (n = 981). We used conditional logistic regression to estimate adjusted odds ratios (ORs) and 95% confidence intervals (CIs). RESULTS: In fully adjusted models incorporating sociodemographic and lifestyle factors, people with cancer registry-notified CUP were more likely to have fair compared with excellent self-rated overall health (OR 1.78, 95% CI 1.01-3.14) and less likely to self-report anxiety (OR 0.48, 95% CI 0.24-0.97) than those registered with metastatic cancer of known primary. Compared to general cohort population controls, people registered with CUP were more likely to have poor rather than excellent self-rated overall health (OR 6.22, 95% CI 1.35-28.6), less likely to self-report anxiety (OR 0.28, 95% CI 0.12-0.63), and more likely to have a history of diabetes (OR 1.89, 95% CI 1.15-3.10) or cancer (OR 1.62, 95% CI 1.03-2.57). Neither tertiary nor community-based health service use independently predicted CUP risk. CONCLUSION: Low self-rated health may be a flag for undiagnosed cancer, and an investigation of its clinical utility in primary care appears warranted.