The well-characterized function of many tumor suppressors is to directly regulate cell cycle events. We recently reported a genetic screen to identify genes that suppress loss of contact inhibition but do not inhibit normal cell proliferation. ING4, one of the genes identified by the screen, is frequently mutated in human cancer, suggesting a role for ING4 as a tumor suppressor. ING4 suppresses tumor cell features such as loss of contact inhibition, cell growth in soft agar, and tumor growth in nude mice. ING4 may belong to a class of tumor suppressors whose function is specific to a tumorigenic event that does not directly involve deregulation of the cell cycle. Studies of these tumor suppressors may provide insight into the molecular mechanisms underlying such tumorigenic events.