HGF and plasma cell myeloma: These effects and other aspects of disease progression are further favored by stroma-secreted cytokines, such as transforming growth factor (TGF)beta [21], insulin-like growth factor 1 (IGF1) [22], interleukin 6 (IL-6) [23], hepatocyte growth factor (HGF) [24], tumor necrosis factor (TNF)alpha [25], Fms-like tyrosine kinase 3 (FLT3) [26], endoglin (CD105) [27], and vascular endothelial growth factor (VEGF) [28], each of whose corresponding tyrosine kinase (TK) receptors serve as targets for several compounds investigated for their anti-myeloma activity.