A 51-year-old female was treated with chemotherapy and pembrolizumab for lung adenocarcinoma and triple-positive breast cancer. They presented to the emergency department two weeks after their second dose of pembrolizumab with abdominal pain, dizziness, diarrhea, and vomiting. Testing indicated elevated glucose above 1123 mg/dL (62.4 mmol/L), elevated ketones, an anion gap of 24 mmol/L, and a pH of 6.94. The patient was diagnosed with DKA and cared for in the ICU with standard insulin therapy and rehydration. Here, INS is linked to lung adenocarcinoma.