Increased Risk of Malignancy in Elderly Patients with Inflammatory Myositis

Abstract

Background/Purpose: The association between inflammatory myositis and malignancy is well established, however, the risk of malignancy in aged patients is known to be similar with general populations. We aimed to analyze the incidence of malignancy in elderly patients with inflammatory myositis, and to estimate the increased risk of malignancy of these patients compared to knee OA patients in Korea.

Methods: Patients with polymyositis (PM) and dermatomyositis (DM) over the age of 50 were identified from Korean nationwide claims database from January 2012 to December 2014 with excluding the patients who had history of any malignancy for a year prior to enrollment. They were observed until any malignancy was newly diagnosed or up to end of the study, December 2015. The crude incidence rate (IR) of malignancies in PM and DM patients over 50 years of age was estimated and we calculated age- and sex-adjusted standardized incidence ratio (SIR) by dividing the observed number of malignancies in patients with PM or DM by expected number of malignancies which was drawn from the incidence rate of malignancy in knee OA patients for cumulative person-years (PYs).

Results: A total of 683 patients with PM and 502 patients with DM over 50 years old were included. In PM patients, 46 cases of solid malignancy (217.7/10,000 PYs) and 4 of hematologic malignancy (18.2/10,000 PYs) occurred during 2,113 and 2,195 PYs of follow-up. On the other hand, the number of 36 solid malignancies (238.0/10,000 PYs) and 7 hematologic malignancies (44.7/10,000 PYs) were identified for 1,512 and 1,565 PYs of observation in patients with DM. Compared to patients with knee OA aged over 50 (n=5,476,302), the risk of overall malignancy was increased in both PM and DM patients; SIR was 1.4 (95% CI 1.0-1.8) in PM patients and 1.8 (95% CI 1.3-2.4) in DM patients, respectively. The risk of solid malignancy was also significantly increased than expected in patients with PM (SIR 1.4, 95% CI 1.0-1.8) and DM (SIR 1.6, 95% CI 1.1-2.1). However, the risk of hematologic malignancy was significantly increased in patients with DM (SIR 9.0, 95% CI 2.3-15.6), but not in those with PM (SIR 3.3, 95% CI 0.1-6.6).

Conclusion: We figure out that even in the elderly patients, inflammatory myositis is associated with increased risk of both solid and hematologic malignancies.