Deep fibromatoses include extraabdominal fibromatosis, or extraabdominal desmoid tumors. The deep fibromatoses are tumors that have the capacity for infiltration and recurrence. The are locally aggressive in nature and may be uncontrollable. They do not metastasize. They are categorized as a benign-aggressive type of tumor. They originate from the deep muscle layers or intramuscular planes within the body. The most common varieties to come to an orthopaedic oncologist's attention include extraabdominal fibromatosis, also known as extraabdominal desmoid tumors, and inflammatory myxohyaline tumor of distal extremities.

Extraabdominal desmoid tumor is an infiltrative tumor that develops in the soft tissues deep to the subcutaneous tissue. Infiltration of skeletal muscle is common. Most patients present with a mass or because of pain, and some patients experience some functional disability. Mot patients are less than 40 years of age, with the majority of those being young adults. This disease, when arising in patients less than 5 years of age, is characterized as infantile fibomatosis.

Most commonly, this tumor involves areas of the shoulder girdle and upper arm, thigh, buttock, and the trunk. Extraabdominal fibromatosis rarely affects the feet and hands. Approximately 10% of those with tumors may have multicentric disease, arising in several different body parts. When multicentricity occurs, almost all of the tumors involve the same extremity. There may be a slight female predilection to the occurrence of this tumor. Extraabomdinal fibromatoses are almost always onfined within muscle and involve the overlying fascia. In very large tumors, extension may occur into the subcutaneous tissues. MRI and CT are important tools in the evaluation of tumor extent in patients with this disease. These tumors do not metastasize, however, they may recur locally. The most reliable means of obtaining local tumor control is by surgical excision with a wide surgical margin. Because these tumors grow in a very infiltrative manner, it is very difficult at the time of surgery to detect microscopic tumor that extends beyond the main mass of the tumor. Thus, a wide margin must be utilized when resecting these lesions. Chemotherapy and radiation may be selectively used for treatment of these tumors. Chemotherapy may be considered preoperatively to shrink the tumors for which surgical resection can result in tissue morbidity. Radiation is often considered as a postoperative modality for eradicating potential microscopic disease. The overall crude local recurrence rate for this disease may be 40-60%, depending on the size of the tumor, anatomic location, patient's age, and prescribed treatment. Local lesions are more prone to recur when compared to those of a smaller volume. The cells in some desmoid tumors contain estrogen receptors, which has prompted the use of various hormonal treatments including tamoxifen. This has been successful in treating some inoperable tumors. NSAIDs have been used with success in that tumor regression is noted following treatment, presumably interfering with prostaglandin production. Rarely, desmoid tumors may spontaneously regress on their own. Presently, there are no characteristics available to clinicians to determine which tumors will regress on their own without intervention. Radiation is typically not recommended as a primary treatment modality, because these tumors are radioresistant. Rarely, patients may die as a result of desmoids tumors, if they invade the head and neck or chest wall, or when they arise in the pelvis and local growth involves critical structures.