Endoscopic Surveillance after (Procto)Colectomy with Gastrointestinal Reconstruction in Patients with Familial Adenomatous Polyposis (FAP)—Principles, Goals and Practical Aspects Based on 12 Years of Observation

(1) Background: Familial adenomatous polyposis (FAP) is a hereditary condition characterized by the development of numerous adenomas in the large intestine, often necessitating colectomy due to an elevated risk of colorectal cancer. Despite surgical intervention, adenomas frequently recur, underscoring the importance of ongoing surveillance. This study evaluates the outcomes of a 12-year endoscopic follow-up after colectomy and gastrointestinal reconstruction for FAP. (2) Methods: A retrospective analysis was conducted on 41 FAP patients who underwent at least one postoperative endoscopic examination. Assessments of the pouch or rectum were performed every 12-18 months following ileorectal anastomosis and every 18-24 months after ileal pouch-anal anastomosis. Follow-up biopsies were assessed using the adopted Spigelman classification. (3) Results: Postoperative pathology revealed invasive colorectal cancer in three patients. Abdominoperineal resection was performed in two cases due to secondary invasive carcinoma, and one T1 tumor was radically removed with ESD. One patient underwent radical pouch excision following a nodal pelvic recurrence of rectal cancer. Over a 12-year observation period, the mean Spigelman score increased by 2 points, and the proportion of patients with low-grade polypoid lesions decreased. The quantity or size of polyps increased in 24 patients, decreased in 8 patients, and remained stable in 9 patients. In four patients, granular, laterally spreading tumors were discovered in the rectal stump. (4) Conclusions: Regular endoscopic surveillance in FAP patients facilitates early identification of neoplastic and inflammatory changes. The downstaging potential highlights the effectiveness of early interventions. While the Spigelman classification assessed polyps well, it did not predict cancer occurrence. A notable number of patients had invasive cancer at the time of surgery, underscoring the importance of early surgical qualification, which is particularly crucial for identifying upstaging or secondary cancer.