Whole blood stem cell reinfusion and escalated dose melphalan in castration-resistant prostate cancer: a phase 1...

Nontaxane-based chemotherapeutic options in castrate-resistant prostate cancer (CRPC) are limited despite the long natural history of the disease. We carried out a phase 1 dose-escalation study of the alkylating agent melphalan with autologous stem cell transplantation, comparing rapid changes in circulating tumor cells (CTC) and prostate-specific antigen (PSA) as a measure of response.

Cohorts of individuals with advanced CRPC received high-dose intravenous melphalan, and autologous blood was returned to patients during treatment. The efficacy endpoints were the PSA reduction rate, CTC response, survival parameters, toxicity and whether reinduction of endocrine sensitivity occurred.

Twenty-four patients were recruited. Dose escalation was feasible with the highest dose cohort being reached. Of 23 individuals evaluable for response, 16 had a PSA response of more than 30%; of 11 patients with soft tissue disease, 4 achieved a partial response and 7 had stable disease. Patients with CTC counts that decreased to less than 5 within 2 weeks from the start of therapy had a longer overall survival (30.6 months vs. 15.3 months, P = 0.03) Treatment was associated with myelosuppression and frequent hospitalizations. In 20 patients after the study, hormone therapy was reintroduced when PSA increased again; response rates were high.

Autologous transplantation following high-dose alkylating agent chemotherapy induces responses but proved toxic, although dose escalation proved possible. The possibility of using CTCs to identify responders at two weeks may be used to justify such an intensive approach. Many individuals went on to further respond to both docetaxel and hormonal therapy.