Cancer incidence among patients with a hospital diagnosis of pruritus: a nationwide Danish cohort study

Background Pruritus is a frequent complaint in patients with cancer. However, no large study has examined pruritus as a marker of undiagnosed cancer. Objectives To examine the association between inpatient, outpatient and emergency hospital diagnoses of pruritus and subsequent cancer diagnoses. Methods In this nationwide Danish cohort study, we used medical databases to identify all patients (n=12813) with a diagnosis of pruritus during the period 1978-2011 and followed them until a first-time cancer diagnosis, emigration, death or 31 December 2011. We computed standardized incidence ratios (SIRs) for cancer as the observed to expected number of cancers based on national cancer incidence rates. We calculated the 1-year absolute risk of cancer, treating death as a competing risk. Results The overall SIR of cancer was 113 [95% confidence interval (CI) 107-120]: 122 (95% CI 113-133) among men and 105 (95% CI 097-114) among women. The SIR was 120 (95% CI 108-133) among patients with a previous diagnosis of dermatological disease and 110 (95% CI 102-118) among patients without such a diagnosis. Both haematological and various solid cancers were observed at increased rates. Overall, the highest SIRs were observed during the first 3months of follow-up, declining rapidly thereafter. The 1-year absolute risk of a cancer diagnosis was 163% and 155 patients with pruritus would have needed to be examined to detect one excess cancer. Conclusions Pruritus may be a marker of occult cancer. Further studies are needed to assess the prognostic benefit of screening for cancer in patients with pruritus.