Local recurrence at anastomotic site presenting as a submucosal tumor-like lesion 23 years after rectal cancer surgery.

Late recurrence of colorectal cancer > 5 years after curative resection is uncommon, and anastomotic local recurrence occurring > 0 years postoperatively is exceedingly rare. We report a case of local recurrence presenting as a submucosal tumor (SMT)-like lesion at the anastomotic site 23 years after surgery for rectal cancer. The patient had a history of rectal cancer surgery and treatment with 5-fluorouracil 23 years prior and presented with a positive fecal occult blood test. Colonoscopy revealed a 15 mm SMT-like lesion with a central depression at the rectal anastomosis. Endoscopic ultrasound (EUS) elastography demonstrated marked stiffness, with an elasticity score of 5. EUS-guided tissue acquisition confirmed adenocarcinoma, and immunohistochemical findings supported the local recurrence. The patient subsequently underwent laparoscopic low anterior resection. Histopathological examination of the resected specimen revealed a diverticulum-like structure formed by invagination of the lamina propria into the submucosa at the previous anastomotic site, with adenocarcinoma identified within this structure; as it was similar to the histopathological findings from the initial surgery. Careful long-term follow-up may be warranted, even in patients who remain recurrence-free for > 5 years after surgery, particularly in cases requiring adjuvant chemotherapy. Furthermore, EUS elastography may be a useful diagnostic modality for SMT-like lesions.