Desmoid tumors are a type of fibromatosis and related to sarcoma, though without the ability to spread throughout the body (metastasize).

The tumors arise from cells called fibroblasts, which are found throughout the body and provide structural support, protection to the vital organs, and play a critical role in wound healing.

The tumors can lead to pain, life-threatening problems, or, rarely, death when they invade other soft tissue or compress vital organs such as intestines, kidneys, lungs, blood vessels, or nerves.

Approximately 10% of individuals with Gardner's syndrome, a type of FAP with extracolonic features, have desmoid tumors.

Desmoid, used by Johannes Peter Müller in 1838, comes from the Greek desmos 'band or tendon-like', describing the tumors' consistency.

"[1] APC mutations affect FAP patients and make up a smaller percentage, 10–15%, of sporadic cases.

[14] The disease has a tendency to occur during and after pregnancy and in exposure to higher estrogen levels, suggesting a hormonal link.

[15] One study noted the formation of desmoid tumors in guinea pigs after prolonged estrogen exposure.

[28] Tumors located intra-abdominally or in the head and neck have the highest risk of mortality due to the proximity to vital structures.

[29] A 3' APC mutation is the most significant risk factor for intra-abdominal desmoid development amongst FAP patients.

[32] A high index of suspicion and a thorough triple examination protocol is necessary to detect rare lesions like a desmoid tumor which can masquerade as breast carcinoma.

[16][24] Desmoid tumors may occur in the head and neck, more commonly among children, and tend to be more aggressive than in other extra-abdominal locations.

[20][18] Tumors may grow, regress, or remain stable:[25] Management of these lesions is complex, the main problem being the high rates of recurrence particularly in FAP-associated disease.

[16] Conversely, for intra-abdominal fibromatosis without evidence of FAP, although extensive surgery may still be required for local symptoms, the risk of recurrence appears to be lower.

As of the 2010s, there is a "clear consensus"[2] from medical groups, including the European Organization for Research and Treatment of Cancer Soft Tissue and Bone Sarcoma Group and the European Society for Medical Oncology: immediate surgical resection is no longer the first-line treatment, particularly in asymptomatic patients.

[15] In more advanced, recurring, or rapidly progressing cases, treatment may consist of complete surgical removal, radiation therapy, antiestrogens (e.g. tamoxifen), nonsteroidal anti-inflammatory drugs (NSAIDs), chemotherapy (e.g. methotrexate and vinblastine or vinorelbine, doxorubicin), or ablation (cold, heat, ultrasound).

Treatment with oral tyrosine kinase inhibitor drugs (e.g. imatinib, sorafenib, pazopanib, sunitinib) shows promising success rates.

[48][49] Patients may need to visit multiple healthcare providers to receive a diagnosis, causing delay in care.

[42] Specific instruments to determine health-related quality of life impacts for desmoid patients, the Gounder/Desmoid Tumor Research Foundation (DTRF) Desmoid Symptom/Impact Scale (GODDESS) and the Desmoid-type fibromatosis Quality of Life Questionnaire (DTF-QOL) have been developed and validated.

[51] A subcategory of D48.1, Neoplasm of uncertain behavior of connective and other soft tissue, has been created with more specific codes:[50] Desmoid tumors occur in dogs, primarily on the head, and more infrequently in horses and cats.