Cancer was a series of diseases in which cells divide in a disorderly manner and behave in a malignant manner. The diseases were one of the most deadly diseases on Earth until the late 21st century, when the scientist Pyong Ko found a method of stopping such growth. (VOY episode: "Fury") Gillian Taylor's mother died of cancer several years before her daughter was transported from 1986 to 2286 along with two hunchback whales named George and Gracie. (TOS - Strange New Worlds VI short story: "Whales Weep Not")