The original Cancer (A.K.A. Jack Klevano) was a criminal mastermind and one of the founding member of the Zodiac Cartel, and had affiliations with Thunderbolts gang. Cancer's base of operations was in Houston, Texas, and the character first appears was in Avengers #72 (1970).
Created by Roy Thomas and Sal Buscema, the first Cancer premiered in Avengers #72 in January of 1970.
Cancer later appears in other issues; such as Ghost Rider #7, Iron Man #184, He dies in West Coast Avengers #26, and is in The Official Handbook of the Marvel Universe [Deluxe Edition] #20. There have been many different characters who have taken the mantle of Cancer afterwords.
A new Cancer has recently appeared in the pages of The Amazing Spider-Man
Cancer appears in The Avengers: United They Stand as a member of the Zodiac. He is depicted as a crab-like alien.