Related narrative: Forequarter Amputation for Malignant Fibrous Histiocytoma
Epidemiology and Risk Factors
Malignant fibrous histiocytoma is the most common histologic type of soft tissue sarcoma (40% of the total). Soft tissue sarcomas can arise almost anywhere in the body; about 50% occur in the extremities (the arms, legs, hands, or feet), 40% in the trunk (chest, back, hips, shoulders, and abdomen), and 10% in the head and neck. Broadly, sarcomas can be classified as arising in bone or from the non-osseous mesodermal derivatives (e.g., muscle, fat, connective tissue).
Sarcomas of the soft tissues can be further grouped into those arising from viscera (gastrointestinal, genitourinary, and gynecologic organs, though not the mucosal layer of hollow viscera in organs) and those that originate in nonvisceral soft tissues such as muscle, tendon, adipose, pleura, synovium, and connective tissue. Soft tissue sarcomas are relatively uncommon cancers. They account for less than 1% of all new cancer cases each year. There are an estimated 8,100 new cases of soft tissue sarcoma in the US annually; however, 4,300 patients die of soft tissue sarcoma-a comparatively high overall mortality rate.
No specific etiologic agent is identifiable in the majority of cases. Occasional cases are related to previous radiation, chemical exposure, alkylating chemotherapeutic agents, or chronic lymphedema. Some reports have suggested that chronic inflammatory processes may be a risk factor for sarcoma (e.g., shrapnel, bullets, intramuscular iron injections, and foreign body implants have been implicated). Recent investigations suggest that genetic factors may play a role in the development of soft tissue sarcoma, involving complex patterns of genetic mutations through unknown mechanisms. Studies have shown that soft tissue sarcomas have specific genetic defects that include allele loss, point mutations, and chromosome translocations. Malignant fibrous histiocytomas are associated with the following cytogenic abnormalities: 1q11, 3p12, 11p11, and 19p13. Inherited diseases that are associated with an increased risk of developing soft tissue sarcomas including neurofibromatosis, tuberous sclerosis, basal cell nevus syndrome, Gardner's syndrome, and Li-Fraumeni syndrome.
Diagnosis and Staging
The majority of patients present with a painless mass, although pain is noted at presentation in up to a third of cases. Delay in diagnosis of sarcomas is common, with the most common incorrect diagnosis for extremity and trunk lesions being hematoma or "pulled muscle." In general, any soft tissue mass in an adult that is asymptomatic or enlarging, is > 5 cm, or persists beyond 4 to 6 weeks should be biopsied. The most favorable imaging of the primary tumor depends on the anatomic site. In the extremities, MRI has been regarded as the imaging modality of choice because it enhances the contrast between tumor and muscle and between tumor and adjacent blood vessels and provides multiplanar definition of the lesion. However, a recent comparison between MRI and CT in patients with malignant bone and soft tissue tumors showed no specific advantage of MRI over CT.
Soft tissue sarcomas are classified histologically according to the soft tissue cell of origin, although the cell type is not part of the prognostic staging system. Additional studies including electron microscopy, histochemistry, flow cytometry, cytogenetics, and tissue culture studies may allow identification of particular subtypes within the major histologic categories.
The American Joint Committee on Cancer (AJCC) has designated staging by the four criteria of tumor size (large = >5 cm), nodal status, histologic grade (how well differentiated), and metastasis. In addition to size, sarcomas are also classified as deep or superficial-superficial located outside the investing muscular fascia without invasion of the fascia, and deep is penetrating through or beneath the investing muscular fascia. Nodal involvement is rare, occurring in less than 3% of patients with sarcoma.
The primary stages are:
Stage IA: low grade, small, superficial, and deep.
A limitation of the present staging system is that it does not take into account the anatomic site of soft tissue sarcomas, which is an important determinant of outcome.
Surgery is the most common treatment for soft tissue sarcomas. If possible, the surgeon removes the tumor and a safe margin of the healthy tissue around it. Depending on the size and location of the sarcoma, it may occasionally be necessary to remove all or part of a limb. However, no more than 10% to 15% of individuals with sarcoma undergo amputation. In most cases, limb-sparing surgery is an option to avoid amputating the arm or leg. In limb-sparing surgery, as much of the tumor is removed as possible, and radiation therapy and/or chemotherapy are given pre or post surgery. In general, every effort is made to achieve a wide margin (2 cm is often an arbitrary choice) around the tumor mass, except in the immediate vicinity of functionally important neurovascular structures, where, in the absence of frank neoplastic involvement, dissection is performed in the immediate perineural or perivascular tissue planes.
The prognosis for patients with adult soft tissue sarcomas depends on several factors, including the patient's age and the size, histologic grade, and stage of the tumor. Older than 60 years of age, tumors > 5 cm, or high-grade histology are associated with a poorer prognosis. While low-grade tumors are usually curable by surgery alone, higher grade sarcomas (as determined by the mitotic index and the presence of hemorrhage and necrosis) are associated with higher local treatment failure rates and increased metastatic potential. For most patients, local control is improved with pre- or postoperative radiotherapy. Despite two decades of randomized trials, the role of postoperative chemotherapy in the management of localized soft tissue sarcoma remains controversial; however, chemotherapy is the mainstay of therapy for patients with metastatic disease.
Local recurrence rates vary depending on the anatomic site of the primary tumor and the adequacy of local therapy; for extremity lesions, approximately 20% of patients develop locally recurrent disease. Treatment of recurrent soft tissue sarcomas depends on the type of initial presentation and treatment. Patients who develop a local recurrence often can only be saved by aggressive local therapy: local excision plus radiation therapy after previous minimal therapy or amputation after previous aggressive treatment.
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