Cancer and pulmonary fibrosis risks in patients with dermatomyositis and polymyositis: A retrospective cohort study

Background This study assessed the risks of developing pulmonary fibrosis and cancer and whether patients are at risk of acquiring subsequent cancer after pulmonary fibrosis development. Methods From the claims data of 22 million insured people, we identified 1461 patients with dermatomyositis (DM) and 1058 with polymyositis (PM) diagnosed in 1996–2016 and 50,380 comparison individuals without pulmonary fibrosis and cancer at baseline, matched by sex and age. Incident pulmonary fibrosis and cancer in each cohort were assessed at the end of 2016. We further followed up individuals with and without pulmonary fibrosis to assess the subsequent development of cancer. Results The cancer incidence was 2.6-fold higher in the DM/PM groups combined than in comparisons (135.3 vs. 52.1 per 10,000 person-years), with an adjusted hazard ratio (aHR) of 3.11 (95 % confidence interval [CI] = 2.71–3.58). The incidence was lower in patients with PM than in those with DM (81.3 vs. 176 per 10,000 person-years), with an aHR of 0.39 (95 % CI = 0.29–0.54). The likelihood of developing pulmonary fibrosis was 92 times higher in the PM/DM groups combined than in comparisons (37.9 vs. 0.41 per 10,000 person-years; aHR 84.0 (95 % CI = 49.5–143). The incidence was 1.44-fold higher in patients with PM than in those with DM (46.1 vs. 32.0 per 10,000 person-years), but the difference was not significant. Further analysis showed that in 2452 patients with myositis without pulmonary fibrosis, 234 (9.5 %) had cancer, whereas no cancer was identified in 67 patients with pulmonary fibrosis (p = 0.019). Conclusion Patients with PM and DM are at great risk of developing cancer and pulmonary fibrosis. Patients who develop pulmonary fibrosis might be at low risk of developing cancer. The complexity of cancer risk interplaying between patients with and without pulmonary fibrosis has clinical relevance and deserves further investigation. Patients who are free of pulmonary fibrosis deserve close monitoring to reduce subsequent cancer risk.