SP and its receptor are expressed in a wide variety of tumor cell lines (WERI-Rb-1 and Y-79 from retinoblastoma, U373 MG and GAMG from glioma, SNK-BE(2), Kelly and IMR-32 from neuroblastoma, CAPAN-1 and PA-TU 8902 from pancreatic cancer, Hep-2 from laryngeal cancer, 23132/87 from gastric cancer, and SW-403 from colon cancer) [65, 67, 137] and tumors such as astrocytomas, gliomas, neuroblastomas, pancreatic cancer, melanomas, and breast cancer [28, 86, 123, 135, 138, 139]. Here, RB1 is linked to central nervous system cancer.