A 62-year-old male receiving pembrolizumab and chemotherapy for their lung adenocarcinoma. The patient received 12 cycles of pembrolizumab and two weeks following the last dose reported vomiting, diarrhea, polydipsia, and excessive thirst. Blood work revealed bicarbonate levels of 12 mmol/L, elevated anion gap of 25 mmol/L, glucose of 600 mg/dL (33.3 mmol/L), and a pH of 7.28. The patient was diagnosed with DKA, managed on an IV insulin drip, and discharged on subcutaneous insulin. The gene discussed is INS; the disease is Polydipsia.