A 70-year-old female underwent follow-up colonoscopy after colonic polypectomy. The colonoscopy revealed the presence of a 7-mm submucosal tumor in the sigmoid colon. The tumor surface was smooth and covered with normal mucosa. It was diagnosed as a submucosal tumor, and polypectomy was performed. Histopathological examination of the resected specimen revealed moderately to poorly differentiated adenocarcinoma measuring 2 × 5 × 3 mm with marked peritumoral lymphocytic infiltration and lymphoid follicle formation. It was diagnosed as carcinoma with lymphoid stroma (lymphoepithelioma-like carcinoma), SM (1,800 μm), ly2, v0, budding; grade 1. We confirmed the indication for noncurative additional surgical resection and performed laparoscopic sigmoid colectomy. No metastases were observed in the dissected lymph nodes.