What happened, in summary

This 67-year-old woman was diagnosed with extensive-stage small-cell lung cancer after imaging showed a right hilar mass, mediastinal lymphadenopathy, pleural effusion, and a 2.4 x 2.2 cm enhancing mass in the pancreatic body concerning for metastasis. Histology of the hilar mass confirmed SCLC. She had chronic obstructive pulmonary disease but no history of diabetes, and baseline HbA1c was within the reference range. She received 4 cycles of carboplatin, etoposide, and atezolizumab, followed by maintenance atezolizumab 1200 mg every 3 weeks. Imaging showed a rapid cancer response: pancreatic MRI at week 7 showed complete resolution of the pancreatic lesion, and chest CT by 14 weeks showed complete remission of thoracic disease. Five months into treatment, she developed autoimmune thyroiditis related to immunotherapy and started levothyroxine. At week 35, after 11 doses of atezolizumab, she developed 4 days of frequent urination, excessive thirst, abdominal pain, and vomiting. Labs confirmed diabetic ketoacidosis. C-peptide was profoundly low, diabetes autoantibodies were negative, and CT showed no pancreatitis, supporting checkpoint inhibitor-associated autoimmune diabetes. She needed prolonged intravenous insulin before transitioning to a basal-bolus insulin regimen, and atezolizumab was stopped while she chose surveillance. Two months later, CT also showed pancreatic volume had decreased by 52%, from 71.4 mL to 37.1 mL. Six months after the diabetes diagnosis, she remained insulin-dependent with ongoing glucose instability. Thirteen months after her initial cancer diagnosis, she developed brain metastases and received whole-brain radiotherapy. Two years after the SCLC diagnosis, she was alive with stable oncologic disease and continued endocrine and oncology follow-up.