A Desmoid Tumor Case that was Difficult to Distinguish from Local Gastric Cancer Recurrence

Abstract

We report a case of a 52-year-old man who underwent a laparoscopic distal gastrectomy with D1+ lymph node dissection and Billroth-I reconstruction for gastric cancer. Histopathological examination revealed poorly differentiated adenocarcinoma with predominant por>tub2 components, pT4a, int, INFc, pPM0, pDM0, ly1, v0, pN0, and cM0, meeting the definition for pathological Stage II B. The patient received eight courses of adjuvant S-1 chemotherapy. Computed tomography (CT) three years after surgery revealed a 45 mm mass adjacent to the remnant stomach. Recurrent gastric cancer was suspected, and five courses of chemotherapy with S-1 and oxaliplatin were administered. The mass increased to 60 mm despite treatment, and surgery was performed for diagnostic and therapeutic purposes. The tumor invaded the remnant stomach and transverse colon, necessitating the en bloc resection of both organs. Histopathological examination confirmed a diagnosis of desmoid-type fibromatosis. Surgical resection often requires the removal of adjacent organs given the locally aggressive behavior of desmoid tumors. An accurate preoperative pathological diagnosis must be established using modalities such as endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) and short-term follow-up with CT to avoid unnecessary chemotherapy or extensive surgery.