PCYT1B and cancer: In cancer, cysteine cathepsins have been identified as important contributors to tumor invasion, angiogenesis, and metastasis [4], most notably CTS B and L. A role for cathepsin B in tumor invasion and metastasis is well described [10, 11]: CTS B localizes to the invasive margin of tumors where it is produced by tumor-associated inflammatory cells [12, 13].