Sarcomatoid carcinomas and variants

Abstract

Introduction The 2004 World Health Organization (WHO) classification of lung tumors defines sarcomatoid carcinomas as a group of poorly differentiated non-small cell lung carcinomas that contain a component of sarcoma or sarcoma-like (spindle and/or giant cells) differentiation. This unifying terminology reflects the similar clinical features of the remarkably different appearing tumors. Five subgroups are recognized, namely pleomorphic carcinoma, spindle cell carcinoma, giant cell carcinoma, carcinosarcoma, and pulmonary blastoma (see Table 1). Sarcomatoid carcinomas are very rare, comprising no more than 2.1% of all lung cancers. This fact has hindered progress in our understanding of these tumors. However, our knowledge of sarcomatoid carcinomas has gradually increased and, in certain aspects, has greatly progressed in recent years. The rationale for this categorization lies in the notion that carcinomas can change their morphological, phenotypic and functional features from an epithelial type to a mesenchymal nature by varying degrees, a phenomenon known as epithelial-mesenchymal transition (EMT). A number of studies on these tumors, including ultrastructural, immunohistochemical and molecular analyses, support this theory.6–17 Epithelial-mesenchymal transition is considered not only a pathological condition but as a fundamental phenomenon essential for embryonic development. In a sense, sarcomatoid change may be regarded as a phenomenon in which certain genetic and epigenetic aberrations lead carcinoma cells to recapitulate an early stage of embryonic development, at which time the primitive epithelial layer gives rise to mesenchymal cells.