Objective: To determine the prevalence and types of malignancy in a large cohort of patients with psoriatic arthritis (PsA), and to compare this rate with that in the general population.
Methods: A cohort analysis of patients who were followed up prospectively from 1978 to 2004 at the University of Toronto Psoriatic Arthritis Clinic was performed. Patients were followed up at 6-12-month intervals according to a standard protocol, which included recording of malignancy, and tracked on a computer database. The cohort was linked with a provincial database to find malignancies that may have been missed by the protocol or developed after patients were lost to followup. Data were presented and analyzed using descriptive statistics and the Cox regression model with robust estimate of variance. Rates of first malignancy in the cohort were compared with rates in the population to derive standardized incidence ratios (SIRs).
Results: Of the 665 patients included, 68 (10.2%) developed a malignancy at an average age of 62.4 years. The most frequently seen malignancies were breast (20.6%), lung (13.2%), and prostate (8.8%) cancer. The SIR for all cancers was 0.98 (95% confidence interval 0.77-1.24). Overall cancer type-specific SIRs were 0.69 (95% CI 0.26-1.83) for hematologic and 0.88 (95% CI 0.46-1.69) for lung cancer. In females, the SIR for breast cancer was 1.55 (95% CI 0.92-2.62), and in males, the SIR for prostate cancer was 0.65 (95% CI 0.29-1.44).
Conclusion: Overall, 10.2% of patients in the Toronto PsA cohort developed cancer. The most frequent cancers were breast, lung, and prostate cancer. The incidence of malignancy in the large PsA cohort did not differ from that in the general population.