Elevated incidence of hematologic malignancies in patients with Sjögren's syndrome compared with patients with rheumatoid arthritis (Finland).

The risk of hematologic malignancies was studied in Finnish patients with rheumatoid arthritis or Sjögren's syndrome, and the difference in the risk between those diseases was evaluated. The study cohorts comprised 676 patients with primary Sjögren's syndrome, 709 with secondary Sjögren's syndrome, and 9,469 with rheumatoid arthritis identified from the Finnish hospitals' national discharge register. The follow-up times were 5,336, 4,254 and 65,391 person-years, respectively. Data on the incidence of malignancies were collected from the files of the Finnish Cancer Registry. The incidence of hematologic malignancies was elevated in the study cohorts. The standardized incidence ratio (SIR) of non-Hodgkin's lymphoma was: 2.2 (95 percent confidence interval [CI] 1.5-3.1) for rheumatoid arthritis; 4.5 (CI = 1.5-11) for secondary Sjögren's syndrome; and 8.7 (CI = 4.3-16) for primary Sjögren's syndrome. The ratio of the SIR of primary Sjögren's syndrome cf rheumatoid arthritis alone was 3.9 (CI = 1.8-8.0) in non-Hodgkin's lymphoma, and 3.4 (CI = 1.2-8.1) in other hematologic cancers. The incidence of hematologic malignancies, especially that of non-Hodgkin's lymphoma, is elevated in patients with rheumatoid arthritis. It is higher in patients with secondary Sjögren's syndrome and highest in patients with primary Sjögren's syndrome. Differences in the immunologic aberration influence oncogenesis.