You need to define "successful" The physician should be fully informative prior to treatment and also determine what are reasonable expectations of treatment. Rarely, with invasive cancers, do we speak of "cures" but period of time in remission or survival time. Some treatments are only meant for palliation and success is in quality of life and not eradication of the cancer.

Let me assume for the purpose of this discussion, that "success" means NO recurrence of the cancer, following treatment. If there is evidence of cancer in the patient, and the expectation was NO EVIDENCE of cancer, then the physician needs to say: "The treatment was not successful" . Then, explain the options available.

I agree with Gerry and Maurice. "Successful" cancer treatments are hard to define. For example, for cancer that has not spread into the lymph nodes and chemotherapy is the course of treatment, if there's no recurrence, the doctor and patient can believe chemotherapy was successful when in reality, the chemo might not have had an effect at all, as the cancer wasn't going to come back anyway.

For example, I had chemo and radiation as part of my invasive-cancer treatment. My cancer had luckily not spread into my lymph nodes. Did the chemo and radiation actually eliminate some stray cells that might have made it into the body? Nobody knows. Yet, people I know assume that chemo and radiation were what saved me.

I'm very grateful for the treatments nonetheless and if I could do it all over again (hopefully I won't ever have to), I would still go through these treatments. The stakes are too high not to.