Development of dermatomyositis after anti-transcriptional intermediary factor 1-γ antibody seroconversion during treatment for small cell lung cancer

BACKGROUND: Inflammatory myositis, such as dermatomyositis, is sometimes complicated by cancer and is recognized as cancer-associated myositis. Although some autoimmune antibodies are considered to be involved in the development of myositis in cancer patients, the precise mechanism has not been clarified. The findings of the present case shed light on the mechanism by which anti-transcriptional intermediary factor 1 (TIF1)-γ Ab was produced and the pathogenesis of cancer-associated myositis. CASE PRESENTATION: We describe a case of dermatomyositis that developed in a 67-year-old man who had been diagnosed with small cell lung cancer of clinical T4N3M0 stage IIIB/limited disease during treatment. He received systemic chemotherapy and radiation therapy, and dermatomyositis developed along with a significant decrease in tumor size. TIF1-γ Ab, which is one of the myositis-specific antibodies, was found to be seroconverted. In addition, immunohistochemical analysis showed that cancer cells were positive for the TIF1-γ antigen. CONCLUSION: The findings of the present case suggest that transcriptional intermediary factor 1-γ, which is released from tumor cells, induces the production of TIF1-γ Ab, leading to the development of dermatomyositis. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12890-022-01974-4.