Abdominal desmoid- course, unique genetic background, and severe outcomes in a large local series.

Abstract

e23544 Background: Abdominal desmoid tumors are locally aggressive, non-metastatic tumors that develop mainly in Familial adenomatous polyposis (FAP) patients, within the mesentery or abdominal wall. Understanding and implications of treatment regimens are evolving. We aimed to assess course, treatment and outcomes of FAP and non-FAP abdominal desmoids and their related genetic alterations. Methods: Retrospective cohort study. Demographics, tumor characteristics, oncological and surgical history, complications, genetic-testing and mortality data were retrieved from two tertiary referral centers. Results: Sixty-two patients were identified (46 FAP, 16 non-FAP) with a median follow up of 72.4 months. Thirty-eight patients (61.3%) underwent surgical procedures: twelve urgent and 26 elective. Out of 33 tumor resections, 39.4% recurred. Hormonal therapy, COX-inhibitors, chemotherapy, imatinib and sorafenib were used in 35(56.4%), 30(48.4%), 18(29.1%), 7(11.3%) and 8(12.9%) of patients, respectively, with 2 years progression-free survival of 67.8%, 57.7%, 38.4%, 28.5%, respectively. Only 1/9 patients treated with sorafenib had disease progression after a median follow up of 6.8 months. Forty-one patients (66.1%) suffered complications: bowel obstruction (30.6%), hyperalimentation (14.5%), ureteral obstruction (12.9%), perforation (11.3%), abscess formation (3.2%) and spinal cord compression (3.2%). Two patients died. Non-FAP patients presented with three renal-cell carcinomas and one germ-cell tumor and carried pathogenic mutations in CHEK2, BLM, ERCC5, MSH6 and PALB2. Conclusions: Abdominal desmoids are mostly FAP-related and are associated with severe outcomes. We report a group of non-FAP abdominal desmoids that includes patients with additional cancer-related gene alterations. This interesting group should undergo genetic consultation and be further explored.