The soft-tissue sarcomas are a group of rare but anatomically and histologically diverse neoplasms. This is due to the ubiquitous location of the soft tissues and the nearly three dozen recognized histologic subtypes of soft-tissue sarcomas. It is estimated that in 2016 approximately 12,310 new cases of soft-tissue sarcoma will be identified in the United States, and 4,990 patients will die of the disease. The age-adjusted incidence is 3.3 cases per 100,000 persons.
Sarcomas constitute less than 1% of all cancers, but 15% of cancers in children, although bone tumors predominate in children. There are familial syndromes in which sarcomas are common, but such genetic conditions are rare.
There is a slight male predominance, with a male-to-female ratio of 1.1:1. Some sarcomas, such as desmoplastic small round cell tumor, demonstrate a distinct male predominance.
The age distribution in adult soft-tissue sarcoma studies is as follows: 20.7% of patients are < 40 years of age; 27.6% are 40 to 60 years old; and 51.7% of patients are > 60 years.
Studies in large cohorts of patients demonstrate that the race distribution of soft-tissue sarcomas mirrors that of the American population (86% Caucasian, 10% African American, 1% Asian American, and 3% other). Some sarcomas, such as Ewing sarcoma, are distinctly unusual in African-American and Asian populations.
Besides issues of ethnicity and the frequency of specific cancers, there are not strong data to indicate a geographical bias in the development of sarcomas.
In the majority of soft-tissue sarcoma cases, no specific etiologic agent is identifiable. However, a number of predisposing factors have been recognized, which are discussed below.
Soft-tissue sarcomas are recognized to originate in radiation fields following therapeutic irradiation for a variety of malignancies. Frequently, they are seen in the lower-dose regions at the edge of the radiation target volume. By definition, radiation-induced sarcomas arise no sooner than 3 years after radiation therapy and often develop decades later; the median time from radiation to development of a soft-tissue sarcoma is 8 to 10 years. The majority of these sarcomas are high-grade lesions (90%), and high-grade undifferentiated pleomorphic sarcoma is a predominant histology. Osteosarcoma, angiosarcoma, and other histologic subtypes have also been reported.
Exposure to various chemicals in specific occupations or situations has been linked with the development of soft-tissue sarcoma. These chemicals include the phenoxyacetic acids (forestry and agriculture workers), chlorophenols (sawmill workers), vinyl chloride (individuals working with this gas, used in making plastics and as a refrigerant), and arsenic (vineyard workers).
Soft-tissue sarcomas have been reported after previous exposure to alkylating chemotherapeutic agents, most commonly after treatment of pediatric acute lymphocytic leukemia. The drugs implicated include cyclophosphamide, melphalan, procarbazine, nitrosoureas, and chlorambucil. The relative risk of sarcoma appears to increase with cumulative drug exposure.
Soft-tissue sarcomas have been noted to arise in the chronically lymphedematous arms of women treated with radical mastectomy for breast cancer (Stewart-Treves syndrome). Lower-extremity lymphangiosarcomas have also been observed in patients with congenital lymphedema or filariasis complicated by chronic lymphedema.
Trauma and Foreign Bodies
Although a recent history of trauma is often elicited from patients presenting with soft-tissue sarcoma, the interval between the traumatic event and diagnosis is often short; thus, a causal relationship is highly unlikely. Chronic inflammatory processes, however, may be a risk factor for sarcoma. Foreign bodies, such as shrapnel, bullets, and implants, have also been implicated.
Signs and symptoms of soft-tissue sarcoma depend, in large part, on the anatomic site of origin. Due to the ubiquitous location of the soft tissues, these malignancies may arise at any site in the body where soft tissues are located. Since 50% of soft-tissue sarcomas arise in an extremity, the majority of patients present with a palpable soft-tissue mass. Pain at presentation is noted in only one-third of cases.
Extremity and Superficial Trunk
Extremity and superficial trunk sarcomas account for 60% of all soft-tissue sarcomas. The majority of patients present with a painless primary soft-tissue mass. Lipomas are at least 100 times more common than soft-tissue sarcomas; however, any growing lesion or even a deep-seated fatty lesion should be biopsied to rule out a sarcoma.
Retroperitoneal sarcomas account for 15% of all soft-tissue sarcomas. Most patients (80%) present with an abdominal mass, with 50% of patients reporting pain at presentation. Due to the considerable size of the retroperitoneum and the relative mobility of the anterior intra-abdominal organs, these tumors often grow to substantial size before the patient's nonspecific complaints are evaluated or even before an abdominal mass is noted on physical examination.
Visceral soft-tissue sarcomas, which comprise 15% of all soft-tissue sarcomas, present with signs and symptoms unique to their viscus of origin. For example, gastrointestinal stromal tumors (GISTs) present with GI symptoms that are usually indistinguishable from those of the more common adenocarcinomas, such as anemia, melena, abdominal pain, or weight loss. Similarly, uterine leiomyosarcomas frequently present with painless vaginal bleeding, such as that often noted in patients with more common uterine malignancies.
Head and Neck
Head and neck sarcomas comprise 10% of all soft-tissue sarcomas. Although generally smaller than sarcomas in other sites, they may present as a palpable mass or with important mechanical problems related to compression or invasion of adjacent anatomy (eg, orbital contents, airway, or pharynx). In addition, their proximity to critical anatomy can pose management difficulties due to compromise in the delivery of both surgery and radiotherapy.
As a consequence of the wide spectrum of soft tissues, a variety of histologically distinct neoplasms have been characterized. The current histopathologic classification is based on the putative cell of origin of each lesion. Such classification based on histogenesis is reproducible for the more differentiated tumors. However, as the degree of histologic differentiation declines, it becomes increasingly difficult to determine a potential cellular origin, and such tumors are usually described by their architecture or cellular morphology, for example, clear cell sarcoma.
In addition, many of these tumors appear to have the ability to dedifferentiate. This process results in a variety of overlapping patterns, making uniform classification difficult. Experienced soft-tissue pathologists frequently disagree as to the cell of origin of an individual tumor. Comparative studies have demonstrated concordance in histopathologic diagnosis in only two-thirds of cases. Malignant fibrous histiocytoma, now termed undifferentiated pleomorphic sarcoma, used to be the most common histologic subtype of soft-tissue sarcoma. However, in one study, reanalysis histologically, immunohistochemically, and ultrastructurally allowed reclassification of most tumors to a specific line of differentiation. GIST is now recognized as the most common form of soft-tissue sarcoma, if all small and relatively inconsequential lesions removed as very early tumors are counted.