That's the fascinating thing about the controversy. There's a cyanide molecule bound up with the laetrile. As long as it's balanced by the laetrile, it's benign to good cells and only harmful to cancer cells because they'r ethe ones with the "receiver" that the cyanide molecule looks for.
The doctor who started the controversy who was pro-laetrile actually shot himself full of it to prove the cyanide wouldn't kill him.