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.

Demographic, social and lifestyle risk factors for cancer registry-notified cancer of unknown primary site (CUP).

BACKGROUND: Little is known about the risk factors for cancer of unknown primary site (CUP). We examined the demographic, social and lifestyle risk factors for CUP in a prospective cohort of 266,724 people aged 45 years and over in New South Wales, Australia. METHODS: Baseline questionnaire data were linked to cancer registration, hospitalisation, emergency department admission, and mortality data. We compared individuals with incident cancer registry-notified CUP (n = 327) to two sets of controls randomly selected (3:1) using incidence density sampling with replacement: (i) incident cancer registry-notified 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 a fully adjusted model incorporating self-rated overall health and comorbidity, people diagnosed with CUP were more likely to be older (OR 1.05, 95% CI 1.04-1.07 per year) and more likely to have low educational attainment (OR 1.77, 95% CI 1.24-2.53) than those diagnosed with metastatic cancer of known primary. Similarly, compared to general cohort population controls, people diagnosed with CUP were older (OR 1.10, 95% CI 1.08-1.12 per year), of low educational attainment (OR 1.69, 95% CI 1.08-2.64), and current (OR 3.42, 95% CI 1.81-6.47) or former (OR 1.95, 95% CI 1.33-2.86) smokers. CONCLUSION: The consistent association with educational attainment suggests low health literacy may play a role in CUP diagnosis. These findings highlight the need to develop strategies to achieve earlier identification of diagnostically challenging malignancies in people with low health literacy.