Lemonhead, I just tried once again to research this, as it has been difficult to pin down. The reports seem to indicate that a specific type of non-Hodgkins lymphoma, Hepatosplenic T-Cell Lymphoma, is occasionally seen in patients on Remicade or Humira
in conjunction with Azathioprine or 6-MP. The reports also say because HSTL is so extremely rare in general and in treated people, there aren't enough statistics to determine what the risk actually is.
I know that studies are continuing, but with an extremely rare form of cancer it could be years or even decades before there is enough data to give firm risk figures. Frustrating but true.