We bring forward a case of a 58-year-old female who, undergoing treatment for glioblastoma with temozolomide and radiotherapy, visited the Emergency Department due to acute abdominal pain and chemotherapy-induced febrile neutropenia. She was diagnosed with sepsis due to phlegmonous gastritis. After several weeks in the Intensive Care Unit with antimicrobial coverage, our patient was discharged. Conceptually, phlegmonous gastritis is a highly unusual bacterial infection of the gastric wall. Intrinsically related to the alteration of the immune system, and frequently linked to cancer patients, its high morbidity and mortality and exceptional casuistry require early treatment and clinical suspicion.