Diabetic Ketoacidosis after Pembrolizumab Treatment in a Patient with Thymic Carcinoma and No Known Diabetes Mellitus: A Case Report

A 64-year-old Chinese man presented in December 2020 with a 3-month history of neck pain.Contrastenhanced magnetic resonance imaging of the cervical spine revealed a large mass at the C6 vertebra (Figure 1).Computed tomography (CT)-guided biopsy of the mass revealed poorly differentiated carcinoma, with immunohistochemistry tests positive for p40, cytokeratin, CD5, PAX8 and c-kit, and negative for thyroid transcription factor 1, CDX2, leukocyte common antigen, S100 protein, desmin, synaptophysin and CD56.These results were suggestive of thymic squamous cell carcinoma.Positron emission tomography-CT showed a hypermetabolic thymic mass and multiple bone metastases, confirming the diagnosis of metastatic thymic carcinoma (Figure 2).No metastases were observed in the pancreas or adrenal glands.He had a past medical history of hypertension well controlled on amlodipine 5 mg daily.His cell counts, organ function, fasting glucose level and lipid profile were normal 1 month before the diagnosis of malignancy.He had no family history of diabetes mellitus.The patient received palliative radiotherapy to the painful cervical and thoracic spine bone metastases at a dose of 22.5 Gy in five daily fractions over 1 week with anterior-posterior opposing fields.The thymic tumour was covered in the radiation portal (Figure 3).Subsequently, he was started on palliative chemotherapy with etoposide and cisplatin (etoposide 100 mg/m 2 and cisplatin 30 mg/m 2 daily from day 1 to day 3 every 3 weeks) in January 2021.Regular zoledronic acid