In this issue we get an update on immunotherapy for prostate cancer. As a reader, you may note that we frequently return to this topic and you may well wonder why? After all, my primary interest has always been on the pharmacology of cancer drugs. The answer is that I have long believed that the goal of treatment should be a long-term complete remission. It has long been evident that this would be difficult to achieve with cancer drugs alone.
By complete remission, we mean that no cancer is visible by any scanning modality and the PSA is undetectable. Note, this does not mean the patient is cancer-free, just that the cancer has been reduced to a microscopic scale and is no longer growing. Why not have “cure” as a goal? As it turns out, “cure” is hard to define in any way that is clinically useful. The best definition I have seen is that it is a complete remission that lasts until the patient dies of something else. In which case, the patient is not “cured” until he has died. Until then, he is in a durable complete remission. Thus, as long as we are dealing with a living patient, a durable complete remission is the best we can hope for.
In prostate cancer, major progress has been made in reducing the amount of cancer in men with metastatic disease, including the frequency of complete remissions. Similarly, the duration of disease control has continued to improve. However, we are far from being able to place a significant proportion of patients into a durable complete remission. In laboratory models of cancer treatment, various immunotherapeutic approaches improve the effectiveness of radiation therapy as well as many drugs. So, it is plausible that immunotherapy may be much more effective in combination than it is as a solo treatment.
Once a patient is in complete remission, the next issue is how to make that remission durable? In other words, how do we keep microscopic residual disease from growing. This area of research is called “cancer dormancy”. In this field, ongoing immune attack on the cancer has proved one of the more consistent successful approaches to maintaining cancer dormancy.
In summary, our continued interest in immunotherapy is based upon the possibility that it might increase the odds of a remission as well as make remissions more durable.
Charles E. Myers, Jr., MD