I'm not saying that all doctors who want to sign you up for their trial are just doing it to have another body. Many if not most, physicians enter patients who they feel would benefit from the trial. That is they are done in many hospitals across the country at the same time. If the trial you are being proposed for is like that, the experiment probably wasn't your doctor's idea to begin with. But it is natural for a doctor to be excited about a new treatment especially if it was his idea.
Clinical trials vary tremendously in their promise.
For this reason, I also think you ought to research all of your options in clinical trials rather than automatically accepting the one your doctor happens to be offering. See CancerGuide information on Finding Clinical Trials and on Understanding the Clinical Trial System . If you have a rare cancer, it definitely pays to get a second opinion. What you really want is to find an expert in that form of cancer. If such an expert is local then you should probably switch to that doctor, if the expert is far away, which is likely, your doctor may be able to work with him via telephone consultations.