Assessment of response to carboplatin in patients with hormone-refractory prostate cancer: a critical analysis of drug activity.

The clinical presentation of prostate-hormone refractory tumours in 90% of patients is characterised by sclerotic bone metastasis which is not assessable by classic phase II response criteria. Restriction of investigational study of new agents to the minority of patients, with bidimensionally measurable lesions, assessable by conventional WHO response criteria, has been criticised because such cases may represent a highly selected tumour cell population. To circumvent this problem, a variety of response criteria have been proposed. However, prostate specific antigen (PSA) levels have become an integral component, used singly or in combination with other markers of response evaluation. As a result, different response proportions could also be reported using the same single agent in this category of patients. This study repors a different evaluation of carboplatin activity by using WHO, NPCP modified criteria and PSA post-therapy decline as measures of carboplatin activity. It is suggested that treatment efficacy in this category of patients wold be more correctly measured by the proportion of patients who "fail treatment" after a reasonable number of therapy courses, rather than those achieving a conflicting definition of "objective response". Finally, in hormone refractory prostate cancer PSA post therapy declines may represent a measure of treatment efficacy and can be used as a surrogate end point for clinical phase II trials.