Systemic sclerosis and cancer in the UK: an epidemiological analysis using the clinical practice research datalink

Background: Cancer can cause mortality in systemic sclerosis (SSc). We investigated the association between cancer and SSc using the Clinical Practice Research Datalink (CPRD). Methods: A validated case-ascertainment strategy identified SSc patients in the CPRD. A cohort study design examined cancer occurrence following SSc, with SSc patients matched to six non-SSc comparators by age, sex and GP practice. Prevalent and incident cases of SSc were analysed separately. Descriptive statistics and Cox analyses determined hazard ratios for cancer occurrence. A case-control study (matched 1:6) examined cancer occurrence prior to SSc. Results: From 10.1 million individuals in CPRD, 1588 of cases of SSc were identified. Two hundred and six cancers followed SSc diagnosis (116 in prevalent and 90 in incident cohort). Commonest cancers were mucocutaneous (4.5%), lung (2.1%) and breast (1.9%). The proportion of SSc patients developing cancer was significantly higher than non-SSc in both incident (11.2% vs 9.7%, P = 0.02) and prevalent cohorts (14.8% vs 12.1%, P = 0.03); particularly for lung cancer (2.6% vs 0.9% in prevalent cohort, P < 0.001). Overall incidence of cancer in the SSc groups was 17.6/1000 person years, compared with 13.9/1000 person years in the non-SSc group. The adjusted hazard ratios for cancer were 1.41 (95% CI 1.14-1.75) and 1.32 (95% CI 1.04-1.67) for prevalent and incident SSc, respectively. No increased risk of cancer prior to SSc diagnosis was identified in the case-control study. Conclusion: We have identified an increased risk of cancer diagnosis following, but not before, SSc diagnosis. Our findings could support screening recommendations for cancer in SSc.