Online Social Meanings, mostly used in forums:
Group of people who encourages more people (hence cancer's spreading nature) go join a certain forum with then corrupts the traditions and influenced (usually in a faggotry sense) the forum.

In other words, Newfags in numbers who couldn't shut up.
The cancer has killed this forum, lets go somewhere else.
by Anonymous asdfasdf July 25, 2008
Get a Cancer mug for your bunkmate José.
Slime videos and any people who try to entertain kids on youtube because they aren't funny. So essentially people who play fortnite and think they're good at it.
NIgga's who play fortnite are cancer
by NothingG.A.Y January 14, 2019
Get a Cancer mug for your dog Manafort.
As far as the Internet is concerned, the term "Cancer" is used to refer to any subject matter, media, page, person, or group of people that incessantly posts idiotic material. This garbage is then reposted endlessly by masses of mindless fans, and is oftentimes unavoidable even to those who don't want to see it. Internet Cancer is unbearably irritating, and currently the only theoretical cure for it is for masses of Big Name sponsored trolls to come together in beautiful unison and spam Cancerous pages into nonexistence.

The Cancerous material that plagues Facebook, Tumblr, Youtube etc., is most often birthed by vapid, shallow celebrities or pseudo-celebrities, since they generally have the highest concentration of like-minded, empty headed fans that will happily spread their cancer and clog the newsfeeds with this garbage.

One example of Internet Cancer is "Brandon Cyrus." Brandon Cyrus is a pseudo-celebrity, whose Facebook fame has given him 326 thousand 'likes.' Despite such a large following, all he ever does is:

1. Shamelessly beg for likes/subscribers

2. Post stereotypical, super-generalized statements that virtually any human being world could "relate to"

3. Make demands of his fans in return for a fake phone number and promises that he'll text them, which fans regularly complain of him never doing.

"Like if you hate being ignored." is an example of a typical Brandon Cyrus post, which are typically liked/shared by thousands of shallow fans.
"Like/Share to save children in Africa from Kony" and not a single child was saved that day.

"Like/Share if you think she's beautiful despite her horrendously disfiguring disease..."

"Like/Share if you think he's cute even though he's obviously incredibly unattractive"

"#YOLO" is an acronym for a cliche phrase "You only Live Once." This phrase has only recently been made cancerous by a vapid celebrity known as Drake.
"#SWAG" is the shortened form of the word "Swagger," that's recently been bastardized and made cancerous by a number of vapid celebrities.

"If you don't repost 1million times you will die in one hour and never find love"

etc.
by Kirika Kure May 06, 2012
Get a Cancer mug for your sister Beatrix.
Kid “can I get fortnite

Dad “ I don’t want you to get cancer to soon tho”
by Nugget101 August 20, 2019
Get a Cancer mug for your brother-in-law José.