Mixed adenoneuroendocrine carcinomas are rare tumors that contain both an exocrine and an endocrine component. Since the latest classification by the World Health Organization and with the aid of immunostaining, more mixed adenoneuroendocrine carcinomas are now identified and diagnosed. Nonetheless, our knowledge of these tumors is still limited, notably concerning gastric variants, as the cases reported in the literature are very limited. The clinical and surgical treatment, including the chemotherapy schemes, the prognosis, and recurrence still represent challenges for the medical teams. We present the case of a 62-year-old woman. After an upper endoscopy revealed multiple polyps and a low-grade neuroendocrine tumor, a D2 radical gastrectomy was performed. A low output esophageal anastomotic leak was discovered in the postoperative period and successfully managed. Pathology revealed a gastric mixed adenoneuroendocrine carcinoma, the first case of this kind reported in Ecuador. Patient is doing well and under constant surveillance up until her 13th postoperative month.