Background: Desmoid tumor (DT) is the primary cause of death in patients with familial adenomatous polyposis (FAP) after restorative proctocolectomy. This study aimed to identify risk factors for DT in a Japanese population. Methods: Clinical data for 319 patients with FAP undergoing first colectomy from 2000 to 2012 were reviewed retrospectively. Results: Two hundred seventy-seven FAP patients were included in this study. Thirty-nine (14.1 %) patients developed DT. Occurrence sites were the intraperitoneal region in 25 (64.1 %) cases, intraperitoneal region and abdominal wall in three (7.7 %), and abdominal wall in nine (23.1 %). The mean period from surgery to DT development was 26.3 months (range 4–120 months). Gender (female vs. male, p = 0.03), age at surgery (>30 vs. ≤30 years, p = 0.02), purpose of surgery (prophylactic vs. cancer excision, p = 0.01), and surgical procedure (proctocolectomy [ileoanal anastomosis (IAA), ileoanal canal anastomosis (IACA), total proctocolectomy (TPC)] vs. total colectomy [ileorectal anastomosis, partial colectomy]; p = 0.03) significantly influenced the estimated cumulative risk of developing DT at 5 years after surgery. Conversely, approach (laparoscopic vs. open, p = 0.17) had no significant effect on the increased risk of DT occurrence. In multivariate analysis, female gender, with a hazard ratio of 2.2 (p = 0.02,) and proctocolectomy (IAA, IACA, TPC), with a hazard ratio of 2.2 (p = 0.03), were independent risk factors for DT incidence after colectomy. Conclusions: Female gender and proctocolectomy (IAA, IACA, TPC) were independent risk factors for developing DT after colectomy in patients with FAP.
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