A 68-year-old male with stage IV sigmoid adenocarcinoma (liver metastases). KRAS and BRAF wild type. No other medical-surgical history of interest. In first line treatment with 5-Fluoracil, oxaliplatin and cetuximab. One week after the administration of the third cycle of therapy, the patient presented vomits which looked like coffee grounds. Gastroscopy showed an esophagus with ulcers, in its proximal third, which converged distally, appearing a black esophagus (Image 1), while gastric cavity had not relevant alterations. On duodenal bulb there were abundant ulcerations in different stages, radially distributed, without active bleeding or visible vessel, suggesting extensive mucositis (Image 2). Acute esophageal necrosis (AEN) is defined endoscopically by a circumferential black-appearing esophageal mucosa with nearly universal involvement of the distal esophagus and abrupt transition at the gastroesophageal junction, with variable proximal extension (1). The 10% of patients with AEN have a history of malignancy (2). Cancer is associated with cachexia and immune dysregulation, thereby decreasing mucosal regenerative ability and increasing susceptibility. AEN often follows chemotherapy administration (1). Mucositis, stomatitis, or esophagopharyngitis (which may lead to mucosal sloughing or ulceration) may occur with fluorouracil (3). In this patient, severity of the adverse event forced the withhold of this drug.