Study Shows Benefits of Adding High-Dose Vitamin D to Chemotherapy for Advanced Prostate Cancer

The addition of high-dose calcitriol (the active form of vitamin D) to weekly treatment with docetaxel (Taxotere) appears to improve response in men with hormone-refractory prostate cancer without compromising safety, according to the results of a study reported at the 38th annual meeting of the American Society of Clinical Oncology (ASCO).

Data from a phase II clinical trial suggest the efficacy of the docetaxel/calcitriolcombination almost doubles compared to docetaxel alone, as measured byprostate-specific antigen (PSA) response rate. The study showed that 81% ofpatients treated with the combination decreased their PSA levels by more thanhalf. Studies of docetaxel without calcitriol have reported a 42% overall PSAresponse rate.

"Because there is no standard treatment for hormone-refractory prostatecancer, new therapeutic strategies are clearly needed," said Tomasz Beer,MD, an oncologist at the Oregon Health and Science University (OHSU) CancerInstitute in Portland, Oregon, and lead investigator of the study. "Docetaxelused alone has shown promise in treating prostate cancer, and our new datastrongly indicate that the favorable results can be enhanced with the additionof high-dose vitamin D."

Tumor Reductions Noted

The study included 37 men with hormone-refractory prostate cancer, or diseasethat was progressive despite standard hormonal therapy, including antiandrogenwithdrawal. In addition to PSA response, 8 of 15 men with measurable disease hadsignificant reductions in tumor size.

Patients in the study received oral calcitriol, 0.5 µg/kg, on the firstday of the treatment cycle, followed by an infusion of docetaxel, 36 mg/m², onthe following day. Treatment was repeated weekly for 6 weeks of an 8-week cycleuntil there was evidence of disease progression or unacceptable toxicity, oruntil the patient requested to be withdrawn from the study.

The results of this phase II study are now the basis for a future phase IIIstudy to be conducted at OHSU and other institutions. That randomized study willevaluate the use of weekly docetaxel vs weekly docetaxel plus calcitriol inpatients with hormone-refractory prostate cancer.