Incidence of lymphoma in a large primary care derived cohort of cases of inflammatory polyarthritis.
OBJECTIVE
To determine the risk of lymphoma in a primary care derived cohort of new onset cases of inflammatory polyarthritis and assess the contribution of disease severity and standard immunosuppressive treatment.


METHODS
Prospective cohort study.


METHODS
2105 subjects with new onset inflammatory polyarthritis were recruited to the Norfolk Arthritis Register (NOAR) and followed annually for (median) 8.4 years. Occurrence of lymphoma was determined by annual morbidity review and linkage to the central hospital database serving the NOAR area. Cases of lymphoma were verified by record review. Standardised incidence ratios (SIRs) for lymphoma were calculated compared with the local, age, sex, and calendar year expected rates. Stratified analyses were undertaken for various markers of disease severity and treatment history.


RESULTS
There were 11 cases of lymphoma during 15,548 person years of follow up, the majority of which were of large B cell type. Compared with the local population the SIR was 2.4 (95% confidence interval, 1.2 to 4.2). The risks in cases classified as rheumatoid arthritis, ever rheumatoid factor positive, or ever treated with DMARDs were all higher, the highest risk group being those treated with methotrexate: SIR = 4.9 (1.8 to 10.6).


CONCLUSIONS
There was a doubling in risk of lymphoma in new onset cases of inflammatory polyarthritis. Patients with the most severe disease were twice as likely as other patients to develop lymphoma. These results need to be taken into account when considering reported increased risks of lymphoma compared to background population risk in users of new biological agents.
Franklin
J
J
ARC Epidemiology Research Unit, Manchester University Medical School, Oxford Road, Manchester M13 9PT, UK.
Lunt
M
M
Bunn
D
D
Symmons
D
D
Silman
A
A
D000293:Adolescent; D000328:Adult; D000368:Aged; D018501:Antirheumatic Agents / Q000009:adverse effects / Q000627:therapeutic use; D001172:Arthritis, Rheumatoid / Q000150:complications* / Q000188:drug therapy / Q000453:epidemiology; D004739:England / Q000453:epidemiology; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D008223:Lymphoma / Q000453:epidemiology / Q000209:etiology*; D008297:Male; D008727:Methotrexate / Q000009:adverse effects / Q000627:therapeutic use; D008875:Middle Aged; D012720:Severity of Illness Index
D018501:Antirheumatic Agents; D008727:Methotrexate