Reappraisal of the incidence, various types and risk factors of malignancies in patients with dermatomyositis and polymyositis in Taiwan

Abstract

Our study aimed to investigate the incidence, risk factors and time to occurrence of malignancy in patients with dermatomyositis (DM) and polymyositis (PM). The electronic medical records of 1100 patients with DM and 1164 patients with PM were studied between January 2001 and May 2019. Malignancies after myositis were diagnosed in 61 (5.55%) patients with DM and 38 (3.26%) patients with PM. The cumulative incidence of malignancies in patients with DM were significantly higher than patients with PM (hazard ratio = 1.78, log-rank p = 0.004). Patients with DM had a greater risk of developing malignancy than those with PM at 40-59 years old (p = 0.01). Most malignancies occurred within 1 year after the initial diagnosis of DM (n = 35; 57.38%). Nasopharyngeal cancer (NPC) was the most common type of malignancy in patients with DM (22.95%), followed by lung, and breast cancers. In patients with PM, colorectal, lung and hepatic malignancies were the top three types of malignancy. The risk factors for malignancy included old age (≥ 45 years old) and low serum levels of creatine phosphokinase (CPK) for patients with DM and male sex and low serum levels of CPK for patients with PM. Low serum levels of CPK in patients with myositis with malignancy represented a low degree of muscle destruction/inflammation, which might be attributed to activation of the PD-L1 pathway by tumor cells, thus inducing T-cell dysfunction mediating immune responses in myofibers. A treatment and follow-up algorithm should explore the occurrence of malignancy in different tissues and organs and suggested annual follow-ups for at least 5.5 years to cover the 80% cumulative incidence of malignancy in patients with DM and PM.

Figure 1

Case number (A), cumulative incidence (B) and the proportion of malignancy (C) in patients with DM and PM after initial diagnosis are plotted against the follow-up period in half-year intervals. The cumulative incidence showed a significant difference between patients with DM and PM based on Kaplan–Meier analysis (hazard ratio = 1.78, log-rank p value = 0.004).

Figure 2

Kaplan–Meier analysis of the malignancy cumulative incidence probability in patients with DM and PM stratified by age, sex and CPK results. Panels (A)–(C) show the malignancy cumulative incidence probability stratified by age, sex and CPK results in patients with DM. Age (≥ 45 years old) showed a significantly higher malignancy incidence (log rank p = 0.001). Panels (D)–(F) show the malignancy cumulative incidence probability stratified by age, sex and CPK results in patients with PM. Male patients had a significantly higher malignancy incidence (log rank p = 0.001). Although the CPK results did not show significant differences based on Kaplan–Meier analyses in patients with DM and PM, there were significant group differences in multivariate Cox regression models (all p < 0.05).