How many members of the manhattan project got cancer?

Hard to say.: This might not ever have an answer since many of the members might have died of other causes, and had cancer and not known it. Also, techniques of diagnosing were not as advenced so it might have gone undiagnosed in several members. In so far as getting cancer from the project itself, this answer may not be known for the above reasons and because so many more people were indirectly involved.