Cancer risk in patients with immunoglobulin A nephropathy: a Swedish population-based cohort study

Background IgA nephropathy (IgAN) is the most common primary glomerulonephritis affecting all ages and both sexes, but there is a lack of studies on its association with cancer and whether it is a paramalignant condition. Methods In a Swedish population-based cohort study we compared the risk of cancer among 3882 biopsy-verified IgAN patients diagnosed during 1974-2011 with 19 341 reference individuals and followed them until 2015. Cox regression was used to estimate hazard ratios (HRs) for cancer in IgAN patients versus controls and conditional logistic regression assessed the risk of cancer before the IgAN was confirmed. Results During a median follow-up of 12.6 years, 488 (12.6%) patients with IgAN and 1783 (9.2%) matched reference individuals were diagnosed with cancer {HR 1.70 [95% confidence interval (CI), 1.52-1.89]}. The increased risk was only seen in IgAN patients developing end-stage renal disease (ESRD), with an HR of 4.01 (95% CI 3.33-4.82) for any cancer and HR of 2.22 (95% CI 1.79-2.75) when excluding non-melanoma skin cancer (NMSC). Non-ESRD IgAN patients did not have an increased overall cancer risk [HR 1.13 (95% CI 0.99-1.30)]. There was no increased risk of cancer preceding an IgAN diagnosis [odds ratio 1.10 (95% CI 0.92-1.32)]. Conclusions We found no support for IgAN being a paramalignant condition. There was an increased risk of cancer in IgAN patients, but only for those with ESRD. Our results indicate similar to 6 extra cancer cases per 100 IgAN patients with ESRD per 10 years, or >17 extra cases if including NMSC as well.