Figure 1: Tumor progression and cathepsin B. (A) Cathepsin B directly degrades ECM constituents such type IV collagen, fibronectin, and laminin [1]. (B) Cathepsin B converts both pro-MMP and pro-uPA to MMP and uPA which results in a proteolytic cascade of further ECM degradation [4]. (C) Cathepsin B converts pre-TGF-β1 to TGF- β1 [11,12] which activates fibroblasts [13]. Fibroblasts release MMP3 which degrades E-cadherin facilitating tumor cell invasion [13,14].