A high dose of calcitrol, the active form of vitamin D, combined with the chemotherapy agent docetaxel, can help the treatment of hormone-refractory prostate cancer, according to research presented at the annual meeting of the American Society of Clinical Oncology (ASCO).
Tomasz Beer, an oncologist at the Oregon Health & Science University (OHSU) Cancer Institute in Portland, Oregon, and lead investigator of the study, told delegates at the meeting that the results of the phase II clinical trial showed that the docetaxel/calcitriol combination could be up to twice as effective as docetaxel alone, as measured by prostate-specific antigen (PSA) response rate.
Beer's study showed that 81 per cent of patients treated with the combination regimen cut their PSA levels by more than half. Studies of docetaxel without calcitriol have reported a 42 per cent PSA response rate overall. PSA is a substance produced within the prostate gland, and a high PSA level may indicate the presence of cancer. In patients with advanced prostate cancer, PSA correlates with the amount of cancer in the body.
"Because there is no standard treatment for hormone-refractory prostate cancer, new therapeutic strategies are clearly needed," said Beer "Docetaxel used alone has shown promise in treating prostate cancer, and our new data strongly indicates that the favourable results can be enhanced with the addition of high-dose vitamin D."
The study included 37 men with hormone-refractory prostate cancer, or disease that was progressive despite standard hormonal therapy, including anti-androgen withdrawal. In addition to PSA response, eight of 15 men with measurable disease responded with significant reductions of their tumours.
Patients in the study received 0.5 mcg/kg of calcitriol on the first day of the treatment cycle, followed by an infusion of 36 mg/m2 of docetaxel on the following day. The treatment was repeated weekly for six weeks of an eight-week cycle until there was evidence of disease progression or unacceptable toxicity, or until the patient requested to be withdrawn from the study.
The results of this phase II study are now the basis for a future phase III study to be conducted at OHSU and other institutions, Beer said. That randomised study will evaluate the use of weekly docetaxel versus weekly docetaxel plus calcitriol in hormone-refractory prostate cancer.