Patterns of care and survival after a cancer of unknown primary (CUP) diagnosis: A population-based nested cohort study in Australian Government Department of Veterans' Affairs clients.

BACKGROUND: Little is known about patterns of care after a cancer of unknown primary (CUP) diagnosis.

METHODS: We performed a retrospective cohort study to describe and compare the treatment, health service use and survival of patients with CUP and metastatic cancer of known primary among 143,956 Australian Government Department of Veterans' Affairs clients, 2004-2007. We randomly matched clients with CUP (C809; n=252) with clients with a first diagnosis of metastatic solid cancer of known primary (n=980). We ascertained health services from the month of diagnosis up to 2 months post-diagnosis for consultations, hospitalizations and emergency department visits, and up to 1 year for treatment. We compared cancer treatments using conditional logistic regression; consultation rates using negative binomial regression; and survival using stratified Cox regression.

RESULTS: 30% of CUP patients and 70% of patients with known primary received cancer treatment and the median survival was 37 days and 310 days respectively. CUP patients received fewer cancer medicines (odds ratio (OR)=0.54, 95% confidence interval (CI) 0.33-0.89) and less cancer-related surgery (OR=0.25, 95% CI 0.15-0.41); males with CUP received more radiation therapy (OR=2.88, 95% CI 1.69-4.91). CUP patients had more primary care consultations (incidence rate ratio (IRR)=1.25, 95% CI 1.11-1.41), emergency department visits (IRR=1.86, 95% CI 1.50-2.31) and hospitalizations (IRR=1.18, 95% CI 1.03-1.35), and a higher risk of death within 30 days (hazard ratio=3.30, 95% CI 1.69-6.44).

CONCLUSIONS: Patients with CUP receive less treatment but use more health services, which may reflect underlying patient and disease characteristics.