CTSB and rheumatoid arthritis: Among various cathepsin derivatives, cathepsin B (CTSB) is considered a potential biomarker for several types of cancers, such as prostate, pancreatic, colon, and breast cancers, as well as for osteoporosis, rheumatoid arthritis, and infectious diseases, and there is good correlation between tumor progression and the CTSB expression [5–8].