Huge Abdominal Desmoid Tumor Successfully Managed by Chemotherapy in a Young Patient With Familial Adenomatous Polyposis: A Case Report.

Familial adenomatous polyposis (FAP) is an inherited disorder characterized by the development of numerous colorectal polyps and an increased risk of extracolonic manifestations, notably desmoid tumors. Desmoid tumors are benign but locally aggressive fibrous neoplasms that do not metastasize but have a high tendency to recur. Due to their rarity, desmoid tumors often present with varied clinical features and nonspecific symptoms. We report the case of a 24-year-old man with no prior medical history who presented in March 2019 with melena, rectal bleeding, and digestive discomfort, without fever or systemic signs. Colonoscopy revealed polyposis, prompting a total colectomy with lymph node dissection in November 2019. Histopathology confirmed approximately 30 tubular adenomas with mild dysplasia; all lymph nodes were free of disease. In October 2020, the patient developed an obstructive syndrome managed by stoma creation, with successful intestinal continuity restoration in February 2021. In May 2021, abdominal swelling led to the discovery of a 17 cm ulcerated mass below the umbilicus. Imaging identified a large necrotic abdominopelvic mass and a smaller intraperitoneal mass. Histological and immunohistochemical analyses confirmed deep fibromatosis (desmoid tumor). The patient received vinblastine and methotrexate chemotherapy, resulting in significant tumor reduction. Subsequently, on September 1, 2023, he underwent extensive tumor resection with lymph node dissection. Pathology confirmed a 7 × 7 × 3.2 cm desmoid tumor with clear margins. This case highlights the critical need for vigilant monitoring in FAP patients, emphasizing early diagnosis and a multimodal treatment approach combining systemic therapy and surgery to effectively manage desmoid tumors.