Sarcoma

PATTERNS OF METASTATIC SPREAD, ORGAN SPECIFICITY, AND TIMING OF RECURRENT DISEASESarcomas are a large and highly heterogeneous family of cancers that share presumptive origins from the mesoderm or endoderm; however, the precise cell of origin for many sarcomas remains unclear [1]. Indeed, an increasingly attractive hypothesis in the field suggests that sarcomas may arise from mesenchymal stem cells [2]. The heterogeneity seen in the family of tumors described as sarcomas may therefore begin as a product of distinct populations of mesenchymal stem cells (defined by maturity, lineage differentiation, and tissues of origin) that are permissive to a variety of oncogenic events. For many sarcomas, specific cancer-associated genes have been defined [3]. These include sarcoma-specific translocations that result in oncogenic fusion genes believed to be necessary for malignant transformation [1, 4, 5]. In sarcomas in which translocations are not present, a complex karyotype is often present, in which driving oncogenic events have been more difficult to define. The biological diversity of the sarcoma family predicts their clinical diversity (Figure 24.1). Sarcomas can be seen in all ages, including pediatric, adult, and geriatric patients. Sarcomas may develop in any organ system and in all anatomic locations. Not surprisingly, and pertinent to this chapter, sarcomas as a family are also associated with a diversity in metastatic biology, and in their responses (or lack of response) to various treatment modalities. As is the case with most solid tumors, the development of metastatic disease in sarcoma patients is the most common cause of death.