Extensive-stage small-cell lung cancer with serplulimab-associated diabetes

What happened, in summary

This 70-year-old man had a long history of smoking and alcohol use but no personal or family history of diabetes. In July 2022, he developed cough and sputum production. Chest CT showed central lung cancer in the right lung with possible obstructive pneumonia and atelectasis, and bronchoscopy with biopsy confirmed extensive-stage small-cell lung cancer. On July 25, 2022, he started serplulimab immunotherapy combined with etoposide and carboplatin. He received 5 cycles through December 2022 and then continued serplulimab monotherapy. During the cancer-treatment period, his blood glucose had not been significantly elevated. On November 5, 2024, he came to the hospital with more than 1 month of dizziness, fatigue, dry mouth, excessive thirst, and frequent urination. Blood testing showed severe metabolic acidosis, blood ketones of 7.3 mmol/L, and glucose of 27.2 mmol/L. HbA1c was 11.9%, fasting and post-meal C-peptide levels were low, and diabetes-associated autoantibodies, including GAD, protein tyrosine phosphatase, zinc transporter 8, and insulin antibodies, were negative. Thyroid tests showed severe hypothyroidism, with very low FT3/FT4 and TSH above the measurable maximum. His team diagnosed immune checkpoint inhibitor-associated diabetes with diabetic ketoacidosis. Serplulimab was stopped during the acute episode, and he was treated with the standard diabetic ketoacidosis protocol, including continuous intravenous insulin, then subcutaneous insulin aspart. He also received oral levothyroxine. After glucose and ketones were controlled, he was discharged after 10 days. He continued insulin therapy and resumed serplulimab, so both endocrine care and lung-cancer treatment remained active. The plan required ongoing monitoring because the diabetes now needed long-term insulin while immunotherapy continued.