Corrections Corporation of America and other private prison companies openly fight efforts to relax drugs laws. Same for prison guard unions; In 2008 the CCPoA, California's largest prison guard union, was the most active opponent of Prop 5, which would have expanded treatment for non-violent drug offenders, and reduced criminal penalties for non-violent drug crimes [1].
As far as I know, oncologists are not fighting cancer research in order to protect their careers.
[1] - https://en.wikipedia.org/wiki/California_Proposition_5_%2820...
Do private prisons fight relaxing laws to make more money? I'm sure some do, but most don't.
Corrections Corporation of America does, and they account for more than 80,000 of the 133,000 private prison beds in the US. GEO Group does, and they account for about 49,000. Together they thus represents the vast majority of private prisons in the US.
Both of them are part of ALEC - a DC base lobbying group that develops model legislation that it then pushes as a means for state legislators to be "tough on crime".
If someone comes up with a cure for cancer, a lot of oncologists are going to be out of a job. Does that mean that oncologists are actively suppressing cancer cures?