Frozen shoulder and risk of cancer: a population-based cohort study

BACKGROUND: Frozen shoulder might be a complication or a presenting symptom of cancer. We examined the risk of a cancer diagnosis after an incident diagnosis of frozen shoulder. METHODS: We used prospectively collected data from Danish registries to identify patients with frozen shoulder during 1995–2013 and followed them for the development of cancer. RESULTS: We observed 2572 incident cancers among 29 098 frozen shoulder patients. The expected number of incident cancers in the general population was 2434. The 6-month cumulative incidence of any cancer was 0.70%, corresponding to a standardised incidence ratio (SIR) of 1.38 (95% confidence interval (CI): 1.19–1.58). Risk increases were highest for lung cancer (SIR=2.19, 95% CI: 1.48–3.13), breast cancer (SIR=1.51, 95% CI: 1.02–2.15), and non-Hodgkin’s lymphoma (SIR=2.28, 95% CI: 1.09–4.20). The cumulative incidence of any cancer during the remainder of follow-up (>6 months to a maximum 18.9 years) was 24.8% with an SIR of 1.04 (95% CI: 1.00–1.08). CONCLUSIONS: Frozen shoulder might be an early predictor for a subsequent cancer diagnosis.