Practice Essentials
Fibrosarcoma is a tumor of mesenchymal cell origin that can occur as a soft-tissue mass or as a primary or secondary bone tumor. In the past, fibrosarcoma was diagnosed much more frequently than it is now; in current practice, it can be more reliably distinguished histologically from similar lesions, such as desmoid tumors, undifferentiated pleomorphic sarcoma, malignant fibrous histiocytoma, [1] malignant schwannoma, and high-grade osteosarcoma.
As with all soft-tissue and bone sarcomas, the mainstay of treatment for fibrosarcoma has been complete excision with an adequate margin; this procedure became prevalent following the publication and wide acceptance of Enneking's surgical principles of musculoskeletal oncology, in the early 1980s. This surgery normally consists of resecting a cuff of normal tissue along with the tumor. Surgical treatment should not proceed unless complete patient care—understood to include biopsy and interpretation of biopsy findings, access to oncologists and radiation oncologists, and definitive resection—is available.
The long-term survival and ultimate functional outcome of fibrosarcoma treatment depend on many interrelated factors. [2, 3] Among these are the size and location of the tumor, its histologic grade, and the presence of metastatic disease (eg, pulmonary metastases). These factors are taken into account with careful evaluation (staging) of the tumor and determine the success of treatment in obtaining good local control and preventing subsequent disease spread.
Continued advances in the molecular biology of sarcomas may further elucidate the very distinct clinical behavior of the various types of fibrosarcoma and ultimately provide better solutions to their respective treatment.
Pathophysiology
Fibrosarcoma is a tumor of mesenchymal cell origin that is composed of malignant fibroblasts in a collagen background. There are two main types: primary and secondary. Primary fibrosarcoma is a fibroblastic malignancy that produces variable amounts of collagen. Fibrosarcoma of bone may be either central (arising within the medullary canal) or peripheral (arising from the periosteum). Secondary fibrosarcoma of bone arises from a preexisting lesion or after radiotherapy to an area of bone or soft tissue. This is a more aggressive tumor and has a poorer prognosis.
Several inherited syndromes are associated with sarcomas. For example, patients with multiple neurofibromas may have a 10% lifetime risk of developing a neurosarcoma or a fibrosarcoma.
The occurrence of fibrosarcoma in conjunction with metallic implants used for fracture fixation or joint reconstruction has been reported, albeit very rarely. [4] The cause of this transformation is unknown.
Preexisting lesions from which secondary fibrosarcoma may arise include bone infarcts and lesions associated with fibrous dysplasia, chronic osteomyelitis, and Paget disease, [5] as well as previously irradiated areas of bone. This form of fibrosarcoma is very aggressive and is associated with a much poorer outcome than that associated with primary fibrosarcoma of bone.
Etiology
No definite cause of fibrosarcoma is known, though genetic mutations may play a role. [6, 7] Research has shown that many sarcomas are associated with such mutations. The more common genetic defects include allele loss, point mutations, and chromosome translocations.
Epidemiology
Fibrosarcoma represents only about 10% of musculoskeletal sarcomas and fewer than 5% of all primary tumors of bone. It can be diagnosed in patients of any age, but it is diagnosed more commonly in patients in the fourth decade of life. It is usually located in the lower extremities, especially the femur and tibia.
Fibrosarcoma of the soft tissues usually affects a wider age spectrum of patients than fibrosarcoma of the bone does, with an age range of 35-55 years. It often arises in the soft tissues of the thigh and the posterior knee. It is generally a large, painless mass deep to fascia and has an ill-defined margin.
An infantile form (in children < 10 years) of fibrosarcoma exists. Unlike fibrosarcoma in adults, it has an excellent prognosis—even in the face of metastatic disease at presentation—when treated with a combination of neoadjuvant and adjuvant chemotherapy and resection. [8, 9, 10, 11]
Fibrosarcoma of bone occurs slightly more commonly in men than in women. No known racial predilection exists.
Prognosis
If all grades are included, primary fibrosarcoma of the bone has a worse prognosis than osteosarcoma, with a 5-year survival rate of 65%. In high-grade primary fibrosarcoma, the 10-year survival rate is less than 30%. Secondary fibrosarcoma is associated with a very poor outcome, the survival rate at 10 years being less than 10%.
For congenital fibrosarcoma of bone in children, the prognosis (which is related to age and to time to diagnosis) is much better, with the disease having long-term survival rates of higher than 50%.
Soft-tissue fibrosarcoma is associated with a 40-60% survival rate at 5 years. The infantile form has an even better 5-year survival rate, in excess of 80%.
Russell et al reported on four patients with infantile fibrosarcoma treated with chemotherapy and surgical resection, all of whom had excellent functional outcome. [8] The patient with fibrosarcoma of the neck displayed rapid tumor shrinkage. Two of the lower-extremity tumors had only modest changes in dimensions, but on resection, the tumor bed contained fibrous tissue with exaggerated small caliber vessels. In the fourth case, metastatic lesions developed in the central nervous system, orbits, lungs, and kidney after complete removal of the primary tumor.
A study using data from the National Cancer Database found that among patients who underwent surgical treatment for fibrosarcoma (N = 2278), overall survival was poorer in older patients with comorbidities, advanced-stage disease, and larger tumors who did not have private insurance and were from areas associated with lower income levels; however, neither neoadjuvant chemotherapy nor neoadjuvant radiation therapy had a significant effect on overall survival. [12]
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Although fibrosarcoma of bone can arise anywhere, it is found most commonly about the knee and femur. The radiograph here shows a typical appearance of a lesion in bone.
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Most pathologists describe the histologic picture of fibrosarcoma as a herringbone pattern. It is an interlacing pattern of sheets of spindle-shaped fibroblasts in a collagen background. This pattern is very distinctive and usually confirms the diagnosis of fibrosarcoma.
