Pneumonia and the incidence of cancer: a Danish nationwide cohort study.

Objectives To examine the risk of a subsequent pulmonary or extra-pulmonary cancer diagnosis following a first-time hospital-based diagnosis of pneumonia. Design Population-based cohort study using Danish medical registries. Setting All hospitals in Denmark. Subjects A total of 342 609 patients with a first-time hospital-based (inpatient, emergency room or outpatient clinic) diagnosis of pneumonia between 1995 and 2011. Main outcome measures We quantified the excess risk of various cancers amongst pneumonia patients compared to the expected risk in the general population, using relative [standardised incidence ratios ( SIRs)] and absolute risk calculations. Follow-up started 1 month after a hospital-based diagnosis of pneumonia and ended on 31 December 2011. Results A total of 28 496 cancers were observed, compared with 21 625 expected, amongst 342 609 pneumonia patients followed for a median of 4.2 years. The absolute risk of a cancer diagnosis 1 to <6 months following a pneumonia diagnosis was 1.4%, with a corresponding SIR of 2.48 [95% confidence interval ( CI) 2.41-2.55]. This was mainly due to an increased risk of lung cancer (eightfold) and haematological cancers (fourfold). The SIR for any cancer remained increased at 1.35 (95% CI 1.30-1.40) during 6-12 months of follow-up, and 1.20 (95% CI 1.18-1.22) during 1-5 years of follow-up. Beyond 5 years, an increased risk was maintained for lung, oesophageal, liver and bladder cancers, squamous cell carcinoma of the skin, lymphoma and multiple myeloma. Conclusions A hospital-based pneumonia diagnosis was associated with an increased risk of a cancer diagnosis, especially in the ensuing months, but the absolute risk was small. [ABSTRACT FROM AUTHOR]