Desmoid Tumour — Rare Non-Cancerous Soft Tissue Growth

Desmoid tumours are mesenchymal clonal proliferations that arise from deep musculoaponeurotic structures throughout the body. Histologically, they consist of well-differentiated, uniform myofibroblastic spindle cells surrounded by abundant collagenous stroma, without the nuclear pleomorphism, high mitotic indices, or necrosis characteristic of malignant sarcomas. Despite their benign histological appearance, their biology is driven by deregulated Wnt/beta-catenin signalling.

Unlike traditional cancers, desmoids lack the capacity to enter lymphatic or circulatory vessels and metastasise to distant sites like the lungs or bones. Nonetheless, their relentless local infiltration can encase major blood vessels, compress nerves, cause severe chronic pain, or penetrate the bowel wall when situated intra-abdominally. Their natural course is highly variable, featuring episodes of rapid growth, protracted stabilization, or spontaneous regression.

Management guidelines for desmoid tumours have undergone a major paradigm shift. In the past, aggressive surgical resection was standard; however, high recurrence rates and post-surgical morbidity prompted experts to adopt active surveillance as the preferred initial strategy. Understanding this modern approach prevents overtreatment. Knowing the tumour's status helps patients weigh active observation against systemic medical therapies, targeted treatments, or local procedures, prioritising long-term functional ability and comfort.

Diagnosis requires core needle biopsy analysed by an experienced sarcoma pathologist to differentiate desmoids from malignant soft tissue sarcomas. Immunohistochemical staining typically shows nuclear accumulation of beta-catenin. Molecular testing frequently reveals somatic mutations in the CTNNB1 gene or germline mutations in the APC gene. Magnetic resonance imaging (MRI) is the primary imaging modality for tracking tumour size, cellularity, and collagen content.

Desmoid tumours are classified under soft tissue tumours (specifically fibroblastic and myofibroblastic neoplasms). They arise in extra-abdominal locations such as the shoulder girdle, chest wall, and thighs, within the abdominal wall, or intra-abdominally in the mesentery. Intra-abdominal desmoids frequently develop in individuals with familial adenomatous polyposis (FAP), a hereditary syndrome linked to germline APC gene alterations.

Initial management generally begins with watchful active surveillance using serial MRI scans. When intervention becomes necessary due to pain, progression, or functional impairment, systemic therapies are preferred over extensive surgery. Treatments include gamma-secretase inhibitors (such as nirogacestat), tyrosine kinase inhibitors (such as sorafenib), anti-oestrogen therapies, non-steroidal anti-inflammatory drugs, or low-dose chemotherapy. Cryoablation represents another emerging local treatment.