The etiology of this tumor remains unclear, although there is an increased prevalence in persons who perform manual labor involving the shoulder girdle. Thus, it has been suggested that repeated trauma by mechanical friction of the scapula against the ribs may induce this process. In up to one third of cases, there is a family history of the tumor, suggesting a nontraumatic genetic origin. Malignant transformation has not been described, and since this process is not a neoplasm but a degeneration of connective tissue, it is not to be expected. Since a number of other tumors including lipomas, metastases, sarcoma, as well as extra-abdominal fibromatosis and hemangioma, may occur on the back and in the subscapular site, it is mandatory to confirm the diagnosis with biopsy.
Morbidity is unexpected.
This condition may occur in persons aged 35-94 years. Clinically, patients usually present with a well-circumscribed large tumor that most often does not adhere to the overlying skin. In one case, ulceration has been described. Uncommon locations include the deltoid muscle, ischial tuberosity, greater trochanter, olecranon, thoracic wall, foot, stomach, mediastinum, orbita, and cornea. Occasionally, the tumor invades the surrounding tissues and becomes fixed to the underlying periosteum.