Novel photodynamic therapy promising for recurrent prostate cancer

NEW YORK (Reuters Health) - Vascular-targeted photodynamic therapy (VTP) using the light-activated drug Tookad offers promise as an effective, minimally invasive salvage therapy for men with recurrent prostate cancer, researchers report.

Tookad (padoporfin, WST09) is a novel palladium-bacteriopheophorbide photosensitizer developed in Israel. Tookad is a Hebrew word suggesting "warmth of light."

In the September issue of BJU International, investigators from Canada and Israel report the results of the largest study to date of Tookad-VTP for whole-prostate ablation in a group of patients with recurrent localized prostate cancer after failure of external beam radiotherapy.

In a phase II trial, a total of 28 men received a 2 mg/kg dose of the photosensitizer and patient-specific light doses as determined by a computer-aided treatment plan, they explain. Under ultrasound guidance, up to six cylindrical light-diffusing delivery fibers were placed transperineally in the prostate.

At high light doses, Tookad-VTP produced large avascular regions in the irradiated prostate, lead investigator Dr. John Trachtenberg from the Ontario Cancer Institute/Prince Margaret Hospital, Toronto and colleagues report.

Specifically, they found that more than half of patients (8 of 13) who received the highest light doses of at least 23 J/cm² in 90% of the prostate had a complete response, "with early MRI evidence of marked prostatic devascularization and no evidence of residual cancer at the 6-month biopsy."

Among these eight patients, PSA levels decreased to negligible levels in men with a baseline PSA level of less than 5 ng/mL.

As expected, side effects of the Tookad-VTP treatment were "modest, generally self-limited, and compared favorably with other salvage methods," the researchers report. Two patients developed rectourethral fistulae, one of which closed spontaneously. The second remains patent more than 6 months out and "continues to manifest itself mainly with intermittent loose stools but with no other significant side effect," the authors note.

Dr. Trachtenberg and colleagues conclude that Tookad-VTP "offers a balance of cancer control and maintenance of quality of life in this difficult group of patients, and this seems better than most other forms of treatment."

"Further clinical trials have been initiated and will determine the exact role of this exciting and promising treatment," they add.

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