Response criteria in prostatic carcinoma.

Assessment of response in advanced prostate cancer is hampered by the preponderance of nonmeasurable, "bone-only" disease. Although bone scans are accurate in assessing new lesions, they are frequently unreliable in evaluating tumor regression. Alternatively, evaluation of response based on changes in prostate-specific antigen (PSA), a biochemical marker, is now routinely incorporated into clinical trials as a surrogate end point for response. However, despite general acceptance of its use as an end point in clinical trials, there is no standardized definition of PSA response. Furthermore, changes in PSA do not always correlate with regression of measurable tumor, especially in response to noncytotoxic agents. PSA changes are most defensibly used to define initial hints of a drug's potential usefulness, rather than as a validation of benefit. Improvement in quality of life has emerged as a clinically relevant endpoint, especially in the setting of hormone-refractory disease, in which therapy has yet to have an impact on survival. There is a current trend toward reporting response to therapy as reflecting changes in biochemical markers, measurable disease, bone-only disease, and quality of life separately, rather than trying to pigeon-hole "response" into traditional categories of "complete" and "partial." This independent reporting of outcome parameters provides a more accurate picture of the potential therapeutic benefit of the assessed new treatments, and allows more informed decision-making by physicians and their patients.