Chapter 094. Soft Tissue and Bone Sarcomas and Bone Metastases (Part 2)

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Chapter 094. Soft Tissue and Bone Sarcomas and Bone Metastases (Part 2) Chapter 094. Soft Tissue and Bone Sarcomas and Bone Metastases (Part 2) Classification Approximately 20 different groups of sarcomas are recognized on the basisof the pattern of differentiation toward normal tissue. For example,rhabdomyosarcoma shows evidence of skeletal muscle fibers with cross-striations;leiomyosarcomas contain interlacing fascicles of spindle cells resembling smoothmuscle; and liposarcomas contain adipocytes. When precise characterization of thegroup is not possible, the tumors are called unclassified sarcomas. All of theprimary bone sarcomas can also arise from soft tissues (e.g., extraskeletalosteosarcoma). The entity malignant fibrous histiocytoma includes many tumorspreviously classified as fibrosarcomas or as pleomorphic variants of othersarcomas and is characterized by a mixture of spindle (fibrous) cells and round(histiocytic) cells arranged in a storiform pattern with frequent giant cells andareas of pleomorphism. For purposes of treatment, most soft tissue sarcomas can be consideredtogether. However, some specific tumors have distinct features. For example,liposarcoma can have a spectrum of behaviors. Pleomorphic liposarcomas anddedifferentiated liposarcomas behave like other high-grade sarcomas; in contrast,well-differentiated liposarcomas (better termed atypical lipomatous tumors) lackmetastatic potential, and myxoid liposarcomas metastasize infrequently but, whenthey do, have a predilection for unusual metastatic sites containing fat, such as theretroperitoneum, mediastinum, and subcutaneous tissue. Rhabdomyosarcomas,Ewings sarcoma, and other small-cell sarcomas tend to be more aggressive andare more responsive to chemotherapy than other soft tissue sarcomas. Gastrointestinal stromal cell tumors (GISTs), previously classified asgastrointestinal leiomyosarcomas, are now recognized as a distinct entity withinsoft tissue sarcomas. Its cell of origin resembles the interstitial cell of Cajal, whichcontrols peristalsis. The majority of malignant GISTs have activating mutations ofthe c-kit gene that result in ligand-independent phosphorylation and activation ofthe KIT receptor tyrosine kinase, leading to tumorigenesis. Diagnosis The most common presentation is an asymptomatic mass. Mechanicalsymptoms referable to pressure, traction, or entrapment of nerves or muscles maybe present. All new and persistent or growing masses should be biopsied, either bya cutting needle (core-needle biopsy) or by a small incision, placed so that it canbe encompassed in the subsequent excision without compromising a definitiveresection. Lymph node metastases occur in 5%, except in synovial and epithelioidsarcomas, clear-cell sarcoma (melanoma of the soft parts), angiosarcoma, andrhabdomyosarcoma, where nodal spread may be seen in 17%. The pulmonaryparenchyma is the most common site of metastases. Exceptions are GISTs, whichmetastasize to the liver; myxoid liposarcomas, which seek fatty tissue; and clear-cell sarcomas, which may metastasize to bones. Central nervous system metastasesare rare, except in alveolar soft part sarcoma. Radiographic Evaluation Imaging of the primary tumor is best with plain radiographs and MRI fortumors of the extremities or head and neck and by CT for tumors of the chest,abdomen, or retroperitoneal cavity. A radiograph and CT scan of the chest areimportant for the detection of lung metastases. Other imaging studies may beindicated, depending on the symptoms, signs, or histology. Staging and Prognosis The histologic grade, relationship to fascial planes, and size of the primarytumor are the most important prognostic factors. The current American JointCommission on Cancer (AJCC) staging system is shown in Table 94-1. Prognosisis related to the stage. Cure is common in the absence of metastatic disease, but asmall number of patients with metastases can also be cured. Most patients withstage IV disease die within 12 months, but some patients may live with slowlyprogressive disease for many years. Table 94-1 AJCC Staging System for Sarcomas Histologic Grade Tumor Size Node Metastases(G) (T) Status (N) (M) Well ≤5 cm (T1) Not Absentdifferentiated (G1) involved (N0) (M0) Moderately >5 cm (T2) Involved Presentdifferentiated (G2) (N1) (M1) Poorly Superficialdifferentiated (G3) fascial involvement ...