CTSS and breast cancer: Cathepsin has been confirmed to be involved in the development of various cancers, including breast cancer,[6] lung cancer,[7] and colon cancer.[8] Cathepsin is known to participate in various cellular functions within the skin, including intracellular protein processing, epidermal homeostasis, and hair development.[9] However, it is still unclear whether cathepsin can cause malignant tumors in the skin.