Objectives Patients with rheumatoid arthritis (RA) have been shown to have an increased risk of developing malignancies. This study was undertaken to determine the incidence and patterns of malignancy in RA patients and identify risk factors of malignancy among patients with RA.
Methods Patients from the TTSH RA Registry were followed up longitudinally and those who developed malignancies from 2001 to 2013 after the onset of RA were identified. Age-standardised rates (ASRs) of various cancers were analyzed and compared with the Singapore Cancer Registry data. Risk factors for developing malignancy, including demographics and disease characteristics at baseline, were analyzed using Chi-squared test and student's t test.
Results Of the 1,134 patients in the registry, 28 patients were excluded as they developed malignancy prior to study enrollment. 1,106 patients were included in the final analysis. Of the 1,106 patients, 81 patients developed malignancies at a mean interval of 15.1 (SD 9.7) years after the onset of RA. The mean age of the 81 patients was 65.9 (SD 10.8) years, of which 61 (75.31%) were females and 69 (85.19%) were Chinese. There were 70 (86.4%) with solid-organ tumours and 11 (13.6%) haematological malignancies.
The ASR of cancer in RA patients was 310.3 for males and 232.5 for females per 100,000 person-years, compared with 229.3 (95%CI 226.5–232) for males and 218.3 (95%CI 213.8–216.3) for females in the general population. By cancer type, there is an increased risk of lung cancer, lymphoid neoplasms and stomach cancer in RA compared with the general population.
The risks factors for developing malignancy (p<0.05) include male gender, non-Indian ethnicity, onset of RA at an older age, untreated RA and higher disease activity.
Conclusions The incidence of solid-organ malignancies was higher than hematological malignancies, unlike that in the literature. The overall risk of malignancy is higher in RA patients. Chronic inflammation from RA is associated with increased risk of malignancy.
Acknowledgement This study is supported by the Centre Grant, National Medical Research Council, Ministry of Health, NMRC/CG/017/2013.
Disclosure of Interest None declared