A ‘Gentle’ Immunotherapy Promising for Advanced Prostate Cancer

NEW ORLEANS-A technique for rallying a prostate cancer patient’s antitumor response helps some patients without harming quality of life, Michael L. Salgaller, PhD, head of the immunothera-peutics division at Northwest Biother-apeutics, Seattle, reported at the 89th annual meeting of the American Association for Cancer Research (AACR).

In this phase II trial, a patient’s own dendritic cells are used to present peptides from prostate-specific membrane antigen (PSMA) to prostate cancer T cells. Dr. Salgaller and his co-workers chose dendritic cells as the delivery medium because "they are very good at stimulating cells of the immune system," he said at a press conference. All the subjects are prostate cancer patients who have failed previous therapies.

The dendritic cells are isolated from a blood sample, grown in the laboratory to a larger volume, exposed to pieces of the patient’s tumor, and then returned to the patient. The goal is for the dendritic cells to activate naïve T cells to be very reactive to prostate cancer, Dr. Salgaller commented.

The protocol calls for six infusions delivered at 6-week intervals. Half of the patients also receive treatment with GM-CSF.

So far, the researchers have treated 104 patients with advanced prostate cancer, with 33 having completed the full treatment. Of these 33 patients, 9 (27%) responded partially, showing some improvement in their disease.

All of the patients started the trial with life expectancies of 6 to 12 months, but some of these partial responders have survived for 2 years, Dr. Salgaller said. In the remaining 24 patients, the cancer stabilized in 11 (33%), while the others showed no response. Seven (21%) of the patients have died, at least six of them from their prostate cancer.

"Our results are promising, but certainly not optimal," Dr. Salgaller said in an interview with Oncology News International. "It’s not surprising that immunotherapy is not 100% effective in this population," he said, pointing out that the immune systems of older men are not as strong as those of younger people, and cancer weakens the immune system further.

"So the extra stimulation provided by immunotherapy still might not be enough to jolt a prostate cancer patient’s immune system into full reactivity to cancer cells," he said. "Also, the treatment parameters may need further refinement."

But Dr. Salgaller found the gentleness of the therapy a big plus for patients who have already been through the wringer with harsh treatments. "It maintains a very good quality of life," he said at the press conference. The side effects have been short term--blood pressure drops, chills, and fevers--and were most common in the first treatment, with later treatments provoking fewer side effects.