BackgroundInterstitial lung disease (ILD) is one of the most common and devastated complication of polymyositis/dermatomyositis (PM/DM). Several studies have focused on serum biomarkers for ILD in PM/DM patients; however, there have been no prospective studies. AimTo explore and compare the predictive value of four serum markers for the development of ILD in patients with PM/DM. MethodsOne hundred adult PM/DM patients were included in this prospective clinical study at baseline. Forty-four PM/DM patients without ILD were followed up for 1 year. Fifty-six PM/DM patients with ILD were treated and followed up for 2 months. Serum samples were analysed for the levels of Krebs von den Lungen-6 (KL-6), monocyte chemotactic protein-1 (MCP-1), surfactant protein-A and D (SP-A, SP-D). ResultsSerum KL-6 (1542.8 760.8U/mL) (P < 0.001), MCP-1 (1870 +/- 1590pg/mL) (P = 0.014), SP-A (56 +/- 28ng/mL) (P < 0.001) and SP-D (230 +/- 196ng/mL) (P < 0.001) were significantly elevated in PM/DM patients with ILD compared with those in the patients without ILD (KL-6 429 +/- 105.8U/mL; MCP-1 1349 +/- 1303pg/mL; SP-A 34 +/- 26ng/mL; SP-D 96 +/- 63ng/mL). In PM/DM patients without ILD who were followed up for 1 year, KL-6 presented the highest predictive value among single markers. In patients who were treated and followed up, KL-6 concentrations increased with the progression of ILD and decreased along with the improvement of ILD. ConclusionConsidering the ability of KL-6 for predicting the onset of ILD and monitoring the treatment response of ILD in PM/DM patients, it may be of great significance for clinical practice, and the prognosis of patients may be substantially improved if serum KL-6 was regularly monitored.