Small Cell Lung Cancer Expressing Glutamate Decarboxylase with Latent Autoimmune Diabetes in Adults.

Small cell lung cancer (SCLC) causes paraneoplastic syndromes, such as diabetes mellitus, by eliciting the expression of various antibodies including anti-glutamate decarboxylase (GAD) antibody. A 62-year-old woman presented to our hospital with a 1-week history of progressive dyspnea and difficulty in walking. Computed tomography showed a tumor obstructing the left bronchus and obstructive lung abscesses with pleural effusions. A biopsy during bronchoscopy revealed SCLC, and the clinical stage was ultimately determined to be IIIB. SCLC was complicated by diabetes mellitus with high titers of serum anti-GAD antibody. An immunohistochemical analysis showed GAD expression in the cancer cells, which is a novel finding.