WEDNESDAY, March 13, 2002 (HealthDayNews) -- Aiming laser light at chemically sensitized pancreatic tumors could be the key to prolonging life among people with this disease.
British researchers report that photodynamic therapy (PDT), in which laser light is delivered directly to cancer cells treated with a photosensitizing drug, significantly improved survival times among a small group of patients with pancreatic cancer.
This is the first report of using PDT to treat pancreatic cancer, and the researchers say the increased survival time points to important clinical implications for the therapy. The findings appear in the March issue of the journal Gut.
The pancreas is a glandular organ behind the stomach that produces enzymes and hormones, including insulin.
Dr. Norman Marcon, director of the University of Toronto's Therapeutic Endoscopy Program, says that while it's difficult to say whether one cancer is worse than another, "[pancreatic cancer] is one of the worst ones to have from the point of view of survival."
Every year, roughly 30,300 Americans develop pancreatic cancer, and roughly 29,700 will die of the disease, largely because they have no symptoms until the cancer is advanced. Those grim statistics make finding a new approach to therapy all the more desirable.
Lead investigator Dr. Stephen Bown, director of the National Medical Laser Center in London, describes PDT as light producing a chemical effect.
"Basically, it's a new way of producing local areas of tissue destruction using a combination of a photosensitizing drug and laser light," says Bown. "There's no heat involved, so it's not like most lasers, and there's no ionizing radiation, so it's not like radiotherapy."
"The reason it's so attractive is that it kills living cells but does not damage the scaffolding that holds tissue together," he says. This means that while it destroys the cancerous cells growing in the pancreas, it leaves the connective tissue that forms the basis of the organ's structure intact, allowing non-cancerous cells to regrow in place of the destroyed tumor.
After testing the therapy on rats and hamsters, the researchers determined the tissues surrounding the pancreas could tolerate PDT. Their next step was to study the effect of the therapy in humans with pancreatic cancer.
Bown and his colleagues enrolled 16 patients between the ages of 46 and 77 with cancer isolated in one region of the pancreas. Before the experiment, all of the patients required a biliary stent procedure to relieve jaundice, a common symptom of pancreatic cancer.
The photosensitizing drug meso-tetrahydroxyphenyl chlorin (mTHPC) was delivered intravenously to the patients, who were then kept in a darkened room for three days to allow the drug to spread and to avoid light reactions.
At that time, each patient was sedated and up to six needles were placed into the deepest part of the tumor. A diode laser inserted through the needles into the tumor delivered red light directly into the tumor.
"Where the light hits, the tumor undergoes necrosis [death]. The mechanism is something called singlet oxygen -- it releases a very localized, short-lived toxin which usually works by destroying the blood supply of the tumor," he explains.
Three patients with progressive pancreatic cancer underwent chemotherapy after the procedure.
All of the patients eventually died of the cancer, but they lived longer. While Bown says the typical patient with localized pancreatic cancer has roughly a 20 percent chance of surviving for one year after surgery, 44 percent of the patients treated in this study were alive one year after the light therapy. Two patients lived for over two years, and one survived for 31 months before succumbing to the disease.
After the procedure, each patient was closely followed in the hospital and after discharge, and returned for monitoring of the tumor. Two patients developed intestinal bleeding that required surgery, 15 of the patients experienced some pain at the site of the drug injection, five patients developed diarrhea that responded to therapy and all 16 developed some skin sensitivity to light. Some patients had more than one symptom.
Marcon adds that normal pancreas cells are uniquely resistant to the damaging effects of PDT, which is crucial given the functional importance of the pancreas gland.
"This treatment was pretty well tolerated, and we could produce destruction of quite a large area of the cancer. The real art in the future is to know exactly how far the tissue destruction will go, and we've still got a lot of research [to do] to refine that."
He says future studies should compare PDT to chemotherapy.
What To Do
Learn more about PDT from the National Cancer Institute or Leeds University.
You can also find out about pancreatic cancer from the American Cancer Society.
