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Doctors Use Light To Fight Cancer
By LAURAN NEERGAARD
AP Medical Writer
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Dr. Marcia Canto uses Photo Dynamic therapy
AP/Gail Burton, File [43K]
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BALTIMORE (AP) -- Dr. Marcia Canto threaded a thin fiber optic line deep into the throat of Jesus Jimenez. The fiber pulsed with bright red light for 12 1/2 minutes, destroying deadly cancer cells without pain and without hurting the healthy esophagus tissue trembling just behind.
Scientists once scoffed at harnessing light to fight cancer and other diseases, but now they say such ''photodynamic therapy'' has potential thanks to potent new drugs that make diseased cells vulnerable to light beams.
The Food and Drug Administration recently approved light therapy to fight advanced esophogeal cancer and early lung cancer. It's not a silver bullet, but it is showing promise against other cancers, too -- with fewer risks than surgery or chemotherapy. It is even being tested against a leading cause of blindness and autoimmune diseases.
''It's pretty exciting,'' Canto said. She was treating Jimenez at Johns Hopkins University Hospital after his doctors in Puerto Rico said operating on the mid-stage tumor was too risky.
It's too early to know Jimenez's prognosis, but his main worry upon leaving the hospital hours later was to guard against a sunburn from the light-sensitive drug left in his system.
''This treatment was so easy, I can't tell you,'' added 83-year-old Walter Winkelmeyer, whose two treatments have left his esophagus cancer-free for six months. ''My doctors had told me I had 18 months to live, and look at me now.''
Winkelmeyer's tumor was caught early, but serious heart and lung problems meant he wouldn't survive any strenuous surgery. Doctors in Sarasota, Fla., said he would die, but relatives discovered Canto also was studying photodynamic therapy, or PDT, in early esophageal cancer.
Doctors have known for nearly 100 years that light could kill. Many drugs are photosensitive -- it's why patients on the antibiotic tetracycline, for example, get sunburned.
The key to making light therapy work was injecting photosensitizers that concentrate in diseased cells but quickly clear out of normal cells -- and then harnessing the right wavelength of light.
Blasting the disease site with a laser's non-burning red light makes the photosensitizer produce a toxic oxygen molecule that kills targeted cells.
''It sounded kind of goofy ... that shining visual light on something would kill a cancer cell. There's been some resistance,'' said Dr. Stephen Hahn, who is testing the method against three intractable cancers -- ovarian, advanced lung and mesothelioma -- at the University of Pennsylvania.
But with recent advances in laser fiber optics and photosensitizers, ''we're seeing a resurgence in interest,'' said George Washington University's Dr. Michael Manyak, who has had success in bladder cancer and now is studying infertility-causing endometriosis.
The government has approved one photosensitizer, Photofrin, by Canada's QLT Phototherapeutics. It doesn't cure advanced esophageal cancer, but regulators determined it offered patients a longer reprieve before throats reclog. Even better, it eliminated early lung cancer in 79 percent of patients.
The drawbacks: the drug takes two days to concentrate in tumors, leaves patients prone to sunburn for six weeks, and penetrates only relatively shallow tumors.
Still, ''anyplace that you can reach with a laser light-delivery system can theoretically be treated with this kind of approach,'' says FDA oncology chief Dr. Robert DeLap.
So companies in the United States, Canada, Japan and England are hunting better photosensitizers -- and other targets.
In the case of macular degeneration, which blinds the elderly, regular lasers can burn away vision-robbing abnormal blood vessels that grow into the eye, but they leave damaging scar tissue and the vessels grow back.
Preliminary experiments suggest therapy every three months with BPD, a next-generation Photofrin, can kill the abnormal blood vessels and block relapse. Now, over 20 North American and European hospitals are searching for proof.
More radical are experiments to see if light therapy affects the immune system to alleviate autoimmune disorders.
QLT treated 20 psoriasis patients inside a body-long light box. Beaming enough light to partially activate the photo-drug but not kill cells, doctors found psoriasis lesions improved enough that the company is pursuing a larger study. |
