- For other uses, see Cancer.
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 humpback whales named George and Gracie. (TOS - Strange New Worlds VI short story: "Whales Weep Not")
One of most extensive forms of cancer was lung cancer, which by the early 21st century was responsible for over a million deaths per year. By the mid 22nd century, lung cancer was easily treatable. The Novan Bernadette Fuller was suffering from lung cancer but Doctor Phlox was easily able to cure her cancer. (ENT episode: "Terra Nova")
Although most forms of cancer were curable by the 22nd century, there were some that still showed up. For unknown reasons, Human males who did not adequately express their emotions were susceptible to it in their middle years. (TOS novel: Spock Must Die!)