Cathepsin B (Cat B) is a lysosomal cysteine protease within normal cells, but is highly up-regulated in cancer cells, particularly at the cancer invasion front, where large amount of Cat B is released from the invading cancer cells to degrade the extracellular matrix, creating a favorable microenvironment for cancer cells migration and metastasis [11, 12]. The gene discussed is CTSB; the disease is cancer.