What is photodynamic therapy?
Photodynamic therapy is also known as photo-chemotherapy, photo-therapy, or photo-radiation therapy, and is based on the discovery that cells or organisms treated with a photo-sensitizing agent can be destroyed by exposure to a specialized light. PDT involves the use of a photo-sensitizing drug, which is either applied to the skin, injected intravenously, or taken orally. After a two or three days, when the drug has been absorbed throughout the body- although more selectively into the cancerous cells, a low-level, fixed-frequency laser light is focused on the tumor which causes the drug to react with oxygen. This forms free radicals or other substances that kill the cancer cells directly, or destroys the blood vessels that feed the cancer cells, or it may also trigger the immune system to begin to attack the cancerous cells. The actual laser treatment can take between 5 to 40 minutes, depending on the area being treated. Since PDT is only useful for treating tumors or pre-cancerous tissues where the laser light can reach, it may not always be practical in some situations. This usually restricts PDT to areas on or lying no more that half an inch beneath the skin, or in the areas of the body that are more accessible, including the lining of internal organs, especially the larynx, esophagus, nasal passages, lungs, stomach, colon, rectum, and bladder. Treatment of prostate, ovarian and pancreatic cancers are still in an experimental stage. Large tumors are more difficult to treat with PDT because the light may not be able to penetrate deeply enough.
In cases where PDT can be used, studies have shown it to be as effective as surgery or radiation therapy at removing cancerous cells. The advantages are that the patient does not have to undergo surgery and the cancer can be very precisely targeted. The treatment can be repeated on the same site (unlike radiation) and the patient can generally be treated as an outpatient. The major drawback with some PDT drugs is that the skin and eyes may become very sensitive to bright light for up to six weeks, or even up to 90 days, requiring special precautions such as avoiding exposure to the sun.
Many specialists remain frustrated that such a cheap and effective treatment which has none of the grueling side effects of chemotherapy is not an automatic option for patients who might easily benefit from this simple procedure. At the moment, PDT is approved by the National Institute for Health and Care Excellence (Nice) in the UK to treat four particular cancers including non-melanoma skin cancer, early or late cancers of the head and neck, lung and cancer of the esophagus. Other areas such as bladder, prostate and brain may be added in the future if the trials that are currently underway turn out to be successful.
It is believed that small, early stage cancers will respond well to PDT and it is also useful for “debulking” large tumors that may be blocking something vital like a windpipe, or as a last resort when other treatments have failed. In all of these areas, PDT has the ability to save patients from having disfiguring surgery and damaging radiation, yet clinicians who use PDT say that it is not being used as often as it could be.
An explanation of photodynamic therapy
Aine Shaw was given photodynamic therapy to treat inoperable lung cancer
It was in 2002 when Aine Shaw was given her deadly diagnosis of inoperable lung cancer. “I had asthma and a weak chest for years and had gone into the hospital with a bad bout of bronchitis,” says the 71 year old former nurse from near Buxton, Derbyshire. She was given an X-ray that revealed that she had a tumor growing in her left lung. “Normally it would have been removed,” she adds. “But my lungs were in such a bad way from the asthma and bronchitis that the surgeon said I probably wouldn’t survive the anesthesia, so they weren’t going to operate.”
Aine was given 18 months to live. “I left hospital to go home and say goodbye to my family. I was in a terrible state. My husband was devastated and so were my two daughters. I had only wanted to see my three grandchildren grow up.” Then a surgeon at the Christie Hospital in Manchester where Aine had been treated told her about a little-known therapy that might have the ability to destroy some of the tumor without having surgery. It is called Photodynamic Therapy (PDT) and it involves a special kind of drug called a photo-sensitizer along with exposure to a special light. Once absorbed into the body’s cells, the drug reacts to the light by producing a highly destructive form of oxygen that is known as singlet oxygen that can destroy a tumor with a single exposure.
There are several different types of sensitizing drugs and each is activated by a light of a different wavelength. The two most common brand names are Foscan and Photofrin. The drugs are either swallowed or injected and then the patient waits for a few hours or days depending on the particulars of the drug that is used. This time period allows the drug to be absorbed by all the cells in the body (including the cancerous cells), which can then be destroyed by exposure to the light. For internal tumors such as the one that was in Aine’s lung, an endoscope with a fine fiber-optic cable attached was passed down her throat to focus a powerful laser beam precisely at the tumor. This procedure was done on an outpatient basis with the patient being sedated for only an hour and she experienced no side effects.
“I had two treatments three months apart, but then the tumor was gone and it’s never come back,” she says. “I couldn’t believe it was so easy. There was no pain and I was back to normal in a few days.” After each treatment, she had to stay out of the sun for a couple of months as exposure too soon could result in nasty blistering.
Aine had her last check-up with Prof Moghissi about a year ago. “I’ve tested her twice a year for the past 10 years, but there has been no sign of a recurrence,” he says. “We had two things to celebrate. She was still alive and she is now a great-grandmother.” It is Aine’s opinion that everyone should know about PDT. “What’s shocking is that most people still don’t.” Aine was treated by Prof Keyvan Moghissi, who is one of the pioneers of PDT in the United Kingdom, at the Yorkshire Laser Center, which is funded by a charitable trust that he set up in 1984. The center now has a partnership agreement to provide PDT throughout Northern Lincolnshire.
This therapy could benefit many more patients with a similar diagnosis like Aine, Prof Moghissi claims. “There are about 4,000 such cases annually,” he says. “At the moment, most of these patients have surgery to remove the tumor, and a few who are too weak or have an inoperable cancer may get PDT. It is only used as a last resort.” But, he argues, PDT should be used used as a first-line treatment for early lung cancer. This is already happening in Japan, where the survival rates are the same as those who have surgery. “PDT is minimally invasive; it doesn’t destroy the underlying tissue and, if necessary, it can be repeated. That’s important if you are treating sensitive areas like the lung or head and neck.”
So with all this going for it, why isn’t PDT being utilized more often? Despite having been around for 30 years and having a number of enthusiastic supporters, critics claim there hasn’t been enough scientific studies testing it against standard treatments. Cancer Research UK warns that caution is needed. This battle over evidence has plagued a review of the effectiveness of PDT that was commissioned in 2008 by Prof Sir Mike Richards, who was then the National Clinical Director for Cancer. Prof Richards promised that if PDT “turns out to offer a better deal than existing treatments, it should soon be available right across the country”. The review, which he expected to report on in 2009, is still ongoing. According to one academic, some experts remain skeptical and are demanding large-scale randomized trials must be performed before they will accept its widespread use.
Aine and her doctors discuss her treatment. This was filmed in 2007.
Clinics that offer photodynamic therapy