Chromosomal Abnormalities
Histologic Classification
        Tumors of fibrous tissue
        Fibrohistiocytic tumors
        Tumors of adipose tissue
        Tumors of smooth muscle
        Tumors of blood and lymph vessels
        Tumors of peripheral nervous system
        Tumors of bone and cartilage
        Tumors of more than one tissue type
        Tumors of unknown histogenesis
Selected Soft Tissue Sarcomas in Children
        Alveolar soft part sarcoma
        Angiosarcoma
        Dermatofibrosarcoma
        Desmoid tumors
        Inflammatory myofibroblastic tumor
        Leiomyosarcoma
        Liposarcoma
        Malignant fibrous histiocytoma
        Malignant peripheral nerve sheath tumor
        Synovial sarcoma
        Undifferentiated soft tissue sarcoma
Biopsy Technique for Soft Tissue Sarcoma
Soft Tissue Sarcoma Tumor Grading System
        Grade 1 lesions
        Grade 2 lesions
        Grade 3 lesions

Nonrhabdomyosarcomatous soft tissue tumors are fairly readily distinguished from rhabdomyosarcoma or Ewing family of tumors; however, classification of childhood nonrhabdomyosarcomatous soft tissue sarcoma (NRSTS) type is often difficult. Obtaining adequate tumor tissue is crucial to allow for conventional histology, immunocytochemical analysis, and other studies such as light and electron microscopy, cytogenetics, fluorescence in situ hybridization, and molecular pathology.[1,2] For this reason, open biopsy (or multiple core-needle biopsies) is strongly encouraged so that adequate tumor tissue can be obtained to allow for all of these crucial studies to be performed.

Many NRSTSs are characterized by chromosomal abnormalities. Some of these chromosomal translocations lead to a fusion of two disparate genes. The resulting fusion transcript can be readily detected by using polymerase chain reaction-based techniques, thus facilitating the diagnosis of those neoplasms that have translocations. Some of the most frequent aberrations seen in nonrhabdomyosarcomatous soft tissue tumors are listed in Table 1.

Pediatric soft tissue sarcomas are classified histologically according to the soft tissue cell they resemble and include the following:[1]

• Fibromatoses (desmoid tumors).
• Adult and infantile fibrosarcoma.
• Dermatofibrosarcoma.

• Malignant fibrous histiocytoma (MFH) (also called undifferentiated pleomorphic sarcoma, or spindle cell sarcoma).

• Liposarcoma.

• Leiomyosarcoma.

• Angiosarcoma.
• Lymphangiosarcoma.
• Hemangiopericytoma.
• Hemangioendothelioma.

• Malignant schwannoma (malignant peripheral nerve sheath tumor [MPNST]).

• Extraosseous osteosarcoma.
• Extraosseous myxoid chondrosarcoma.
• Extraosseous mesenchymal chondrosarcoma.

• Malignant mesenchymoma.
• Malignant Triton tumor.[8]
• Malignant ectomesenchymoma.[9]

• Alveolar soft part sarcoma (ASPS).
• Epithelioid sarcoma.
• Clear cell sarcoma (malignant melanoma of soft parts [MMSP]).
• Synovial sarcoma.
• Desmoplastic small round cell tumor.[7]

This is a tumor of uncertain histogenesis. A consistent chromosomal translocation t(X;17)(p11.2;q25) juxtaposes the ASP gene with the TFE3 gene.[5] ASPS almost never has an objective response to chemotherapy.[10] In children, ASPS often presents with metastases,[11] and sometimes has a very indolent course. There are single case reports of objective responses to interferon-alpha and to bevacizumab.[12,13]

A review of 20 years of experience in the Italian and German Soft Tissue Sarcoma Cooperative Group identified 12 children with angiosarcoma.[14] Only one objective response to chemotherapy was observed, and the overall behavior of this tumor was identical to angiosarcoma in adults.

Dermatofibrosarcoma is a rare tumor, but many of the reported cases arise in children.[15] The tumor has a consistent chromosomal translocation t(17;22)(q22;q13) that juxtaposes the COL1A1 gene with the PDGF-beta gene. Most tumors are cured by surgical resection. When surgical resection cannot be accomplished or the tumor is recurrent, treatment with imatinib has been effective.[16]

Desmoid tumors are low-grade malignancies with very low potential to metastasize. The tumors are locally infiltrating, and surgical control can be difficult because of the need to preserve normal structures. These tumors also have a high potential for local recurrence. Desmoid tumors have a highly variable natural history, including well documented examples of spontaneous regression.[17] Repeated surgical resection can sometimes bring recurrent lesions under control.[18]

Inflammatory myofibroblastic tumor (IMT) is an incompletely characterized neoplasm of intermediate biologic potential. It recurs frequently but metastasizes rarely.[19] Roughly half of IMTs exhibit a clonal mutation that activates the anaplastic lymphoma kinase (ALK)-receptor tyrosine kinase gene at chromosome 2p23.[20] There are no well-documented responses to chemotherapy. There are case reports of response to either steroids or non-steroidal anti-inflammatory drugs.

A 24-year retrospective analysis of the Italian cooperative group identified one child with leiomyosarcoma.[21] A retrospective analysis of the St. Jude Children’s Research Hospital experience from 1962 to 1996 identified 40 children with NRSTS; none had leiomyosarcoma.[22] Among 43 children with HIV/AIDS who developed tumors, eight developed Epstein-Barr virus–associated leiomyosarcoma.[23]

A 24-year retrospective analysis of the Italian cooperative group identified two children with liposarcoma.[21] The tumors did not respond to chemotherapy. Outcomes were the same as those observed in adults with liposarcoma.[24]

At one time, MFH was the single most common histiotype among adults with soft tissue sarcomas. Since it was first recognized in the early 1960s, however, MFH has been plagued by controversy in terms of both its histogenesis and its validity as a clinicopathologic entity. The latest World Health Organization classification no longer includes MFH as a distinct diagnostic category but rather as a subtype of an undifferentiated pleomorphic sarcoma.[25]

MPNST arises in children with type 1 neurofibromatosis (NF1), and it arises sporadically.[26] Features with favorable prognosis have been reported to include absence of NF1, less invasiveness, lower stage, and an extremity as the primary site.[26,27] Chemotherapy has achieved objective responses in childhood MPNST. The role of adjuvant chemotherapy following resection of MPNST has not been prospectively evaluated. A retrospective survey of cancer centers in Japan identified 56 patients with MPNST, mostly adults, but including children and adolescents.[28] This survey identified large tumor size, metastasis at presentation, and high histologic grade as unfavorable prognostic features. In this report, documentation of NF1 did not confer an inferior prognosis.

Synovial sarcoma is considered to be more chemotherapy responsive than many other soft tissue sarcomas. There is ample documentation of objective responses of synovial sarcoma to systemic chemotherapy.[21,29-31] The value of adjuvant chemotherapy following resection of localized disease has not been conclusively supported in prospective trials, but most pediatric oncologists favor adjuvant chemotherapy for all but the smallest, completely resected tumors.[30,32-34]

Diagnosis of synovial sarcoma is made by immunohistochemical analysis, ultrastructural findings, and demonstration of the specific chromosomal translocation t(x;18)(p11.2;q11.2). This abnormality is specific for synovial sarcoma and is found in all morphologic subtypes. Synovial sarcoma results in rearrangement of the SYT gene on chromosome 18 with one of the subtypes (1, 2, or 4) of the SSX gene on chromosome X.[35,36] Synovial sarcoma can be subclassified as monophasic fibrous type, biphasic type with distinct epithelial and spindle cell components, or poorly differentiated. Poorly differentiated synovial sarcoma has features of monophasic or biphasic synovial sarcoma but also a variable proportion of poorly differentiated areas characterized by high cellularity, pleomorphism, and polygonal or small round-cell morphology, numerous mitoses, and often necrosis.[37]

Patients with undifferentiated sarcoma have been eligible for participation in rhabdomyosarcoma trials coordinated by the Intergroup Rhabdomyosarcoma Study Group and the Children’s Oncology Group. The rationale for this inclusion was the observation that patients with undifferentiated sarcoma have similar sites of disease and outcome to those with alveolar rhabdomyosarcoma. In therapeutic trials for adults with soft tissue sarcoma, patients with undifferentiated sarcoma are included with all other histologies and treated in a similar manner. Contemporary treatment for adult soft tissue sarcoma utilizes ifosfamide and doxorubicin, sometimes with the addition of other chemotherapy agents, surgery, and radiation therapy. No data are available to compare these two approaches.

When a suspicious lesion is identified it is crucial that a complete workup followed by adequate biopsy be performed. Generally, it is better to image the lesion prior to any interventions. A core-needle biopsy or limited open biopsy that obtains an adequate amount of tissue for histopathology, immunohistochemistry, and molecular genetics is mandatory, given the diagnostic importance of translocations. Image-guided needle biopsy techniques must also obtain an adequate tissue sample and usually require obtaining multiple cores of tissue. Incisional biopsies are acceptable but should not compromise subsequent wide local excision. Transverse extremity incisions should be avoided to reduce skin loss, as should extensive surgical procedures prior to definitive diagnosis.

In most cases, accurate histopathologic classification of soft tissue sarcomas alone does not yield optimal information about their clinical behavior. Therefore, several histologic parameters, including degree of cellularity, cellular pleomorphism, mitotic activity, degree of necrosis, and invasive growth, are evaluated in the grading process. This process is used to improve the correlation between histologic findings and clinical outcome.[38] In children, grading of soft tissue sarcomas is compromised by the good prognosis of certain tumors such as infantile fibrosarcoma. In addition, testing of a grading system within the pediatric population is difficult because of the rarity of these neoplasms. In March 1986, the Pediatric Oncology Group conducted a prospective study on pediatric soft tissue sarcomas other than rhabdomyosarcoma and devised the grading system that is shown below. Analysis of outcome for patients with localized soft tissue sarcomas other than rhabdomyosarcoma demonstrated that patients with grade 3 tumors fared significantly worse than did those with grade 1 or grade 2 lesions. This finding suggests that this system can accurately predict the clinical behavior of nonrhabdomyosarcomatous soft tissue tumors in children.[2,38,39]

• Myxoid and well-differentiated liposarcoma.
• Deep-seated dermatofibrosarcoma protuberans.
• Well-differentiated or infantile (patient 4 years or younger) fibrosarcoma.
• Well-differentiated or infantile (patient 4 years or younger) hemangiopericytoma.
• Well-differentiated malignant peripheral nerve sheath tumor.
• Extraosseus myxoid chondrosarcoma.
• Angiomatoid malignant fibrous histiocytoma.

In grade 2 lesions, which are soft tissue sarcomas not included in grade 1 and grade 3 lesions, less than 15% of the surface area shows necrosis, and there are fewer than five mitotic figures per ten high-power fields (40X objective). As secondary criteria of grade 2 tumors, the incidence of nuclear atypia is not marked, and the tumor is not markedly cellular.

• Pleomorphic or round cell liposarcoma.
• Mesenchymal chondrosarcoma.
• Extraosseous osteosarcoma.
• Triton tumor (MPNST with rhabdomyosarcomatous elements).
• Alveolar soft part sarcoma.
• Synovial sarcoma.
• Epithelioid sarcoma.
• Clear cell sarcoma (MMSP).

Any other sarcoma not included in grade 1 in which more than 15% of the surface area is necrotic or in which there are more than five mitotic figures per ten high-power fields (40X objective) is considered a grade 3 lesion. Marked atypia and cellularity are less predictive but may assist in placing tumors in this category.

References

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