Risk of desmoid tumor based on APC pathogenic variant location and surgical history in familial adenomatous...

Desmoid tumors (DT) are a leading cause of morbidity and mortality in patients with familial adenomatous polyposis (FAP), yet available data on DT risk remain limited and have been largely derived from large registries or tertiary referral centers. Risk in community-based U.S. populations is poorly defined, which hinders presurgical counseling. We conducted a retrospective cohort study of patients with pathogenic or likely pathogenic variants (PV/LPV) in APC identified through the Kaiser Permanente Northern California Electronic Database, a community-based system serving 4.6 million members. We evaluated the association of APC PV/LPV location and prior abdominal surgery with DT risk using multivariable logistic regression, adjusting for sex, race and ethnicity, and family history. Among 328 patients with FAP, 36 (11.0%) developed DT. DT risk was highest when the APC variant was centrally located (codon 600-1600). Family history was independently associated with increased risk (adjusted odds ratio [aOR] 4.34; 95% confidence interval [CI] 1.12-16.86). All colorectal surgeries were associated with a significantly elevated DT risk: ileostomy (aOR 12.07; 2.10-69.47), subtotal colectomy with ileorectal anastomosis (aOR 9.03; 1.63-49.96), and total proctocolectomy with ileal pouch-anal anastomosis (aOR 10.98; 2.12-56.81). In contrast, non-colorectal surgery was not associated with increased risk (aOR 0.73). In this large community-based U.S. cohort, central APC variant location, family history, and colorectal surgery were associated with increased DT risk. Our findings extend the current literature on DT risk in FAP and help refine presurgical risk-stratification and counseling for these patients.