The Risk of Malignancy in Korean Patients with Rheumatoid Arthritis

To investigate the overall cancer risk and risk for specific cancers in rheumatoid arthritis (RA) patients in Korea by comparing cancer incidence between RA patients and the general population.

Individuals diagnosed with RA between 1996 and 2009 who underwent treatment at the Daegu Catholic University Medical Center were retrospectively examined. 1885 patients with RA were included in the analyses. Occurrence of cancer and death during follow up was ascertained by linking medical records to the Korean Central Cancer Registry and national death certificates. For comparing cancer incidence between RA patients and general population, standardized incidence ratios (SIR) were calculated. The 95% confidence intervals (CIs) of SIRs were calculated using the shortcut method introduced by Vandenbroucke.

The total follow-up time was 10218.9 person-years. During follow up, 100 patients (31 men and 69 women) were diagnosed with cancer. Both men and women had greater risks of having malignancy, although cancer risk was greater in men. Men showed increased risks of lung cancer (SIR=5.46, 95% CI: 2.60-9.36) and leukemia (SIR=16.7, 95% CI: 1.58-47.9). Women showed increased risks of thyroid cancer (SIR=1.75, 95% CI: 1.02-2.68), cervical cancer (SIR=3.65, 95% CI: 1.65-6.42), non-Hodgkin's lymphoma (SIR=6.47, 95% CI: 2.04-13.4), and gallbladder cancer (SIR=3.87, 95% CI: 1.01-8.60). Disease-modifying anti-rheumatic drugs usage and cancer were not related: the relative risks of developing malignancy were not elevated for each medicine.

The overall cancer incidence was increased in Korean men and women with RA. Increased risk of specific malignancy differed according to sex.