Cancer Black is a total conversion mod for AvP Gold, taking place between 1999-2004. It was created by the AMP Team, led by Eldritch (Christoffer Lundberg). Other members include AvP, Droneboy, Glock, Kipling, Oblivion, Reb Lev, S_Hole, Sammer, Scythewraith, and TJ72. AvP, Glock, Oblivion, Sammer, and TJ72 are not credited in the release v.1.1 (2003).
It is the most extensive mod for AvP as it changes a great number of gameplay aspects, adds new models and maps, has its own single-player campaign, features new playable species, and overall completely changes the feel of the game. The best description I can come up with for the mod is that it "AvP2-izes" AvP1. That is, it basically takes all the features that Monolith changed from AvP1 to AvP2 and tries to recreate them in AvP Gold. This isn't a perfect one-to-one analogy--after all, the mod does use its own original maps--but the similarities are too great to disregard. The gameplay is significantly slower, the marine has many more tools, such as a welder and a limited number of flares, there's a walk/run toggle, the alien pounces, there's a life-cycle mode, the predator has more weapons (many of which feel random), such as the netgun and combi-stick, the multiplayer is more team-based, requiring communication and coordination, and it also has vehicle-riding levels. Although it only works if you have Gold Edition, you can get it running if you have an old enough version of DirectX or if you use the dgVoodoo fix.