The Vitamin B17 molecule contains 2 units of glucose and 1 benzaldehyde and 1 cyanide.
Only the enzyme beta-glucosidase can unlock the cyanide and benzaldehyde.
The cancer cell doesnt contain the protecting enzyme Rhodanese therefore the cyanide and benzaldehyde is released only in the cancer cell, killing only the cancer cell.
"World without cancer" by G. Edward Griffin
And numerous online sources
http://www.bibliotecapleyades.net/salud/salud_defeatcancer09.htm
http://www.bibliotecapleyades.net/salud/salud_defeatcancer25.htm