Abstract
Synchronous gastric cancer with another neoplasm is a rare condition, with colorectal cancer being the most frequently associated neoplasm. This article presents a case of a 76-year-old male diagnosed with synchronous gastric and rectal cancer with complete remission of gastric and rectal neoplasms after adjuvant therapy. The patient exhibited symptoms prompting upper and lower endoscopies, revealing gastric and rectal adenocarcinomas, respectively. Staging was performed, and due to the locally advanced nature of both malignancies, the patient underwent total neoadjuvant therapy (TNT) for rectal cancer. The treatment consisted of external radiotherapy and neoadjuvant chemotherapy with oxaliplatin, leucovorin, folinic acid, and fluorouracil (FOLFOX). Remarkably, after seven cycles, a complete clinical response of the rectal neoplasm was achieved. Subsequent surgical resection included simultaneous subtotal gastrectomy and rectal anterior resection, resulting in a complete pathological response for both tumors. To the best of our knowledge, it is among the first cases to report a full pathological response in gastric cancer following TNT intended for rectal cancer.