Knee and hip osteoarthritis and risk of nine cancers in a large real-world matched cohort study

Objectives Joint replacement due to end-stage OA has been linked to incidence of several cancers. We aimed to estimate the association between newly diagnosed knee and hip OA and incidence of nine common cancer types. Methods We identified persons with incident knee or hip OA, aged >= 40 years, between 2009 and 2015 in the SIDIAP database in Catalonia, Spain. We matched up to three OA-free controls on age, sex and general practitioner. We followed participants from 1 year after OA diagnosis until migration, death, end of study at 31 December 2017 or incident cancer of: stomach, colorectal, liver, pancreas, lung, skin, breast, prostate and bladder. We used flexible parametric survival models, adjusted for confounders. Estimates were corrected for misclassification using probabilistic bias analysis. Results We included 117 750 persons with knee OA and matched 309 913 persons without, with mean (S.d.) age of 67.5 (11.1) years and 63% women. The hip cohort consisted of 39 133 persons with hip OA and 116 713 controls. For most of the included cancers, the hazard ratios (HRs) were close to 1. The HR of lung cancer for knee OA exposure was 0.80 (95% CI: 0.71, 0.89) and attenuated to 0.98 (0.76, 1.27) in non-smokers. The hazard of colorectal cancer was lower in persons with both knee and hip OA by 10-20%. Conclusions Knee and hip OA are not associated with studied incident cancers, apart from lower risk of colorectal cancer. The often-reported protective association of knee OA with lung cancer is explained by residual confounding.