When cancer forms in the esophagus, it begins in the innermost layer of the tissue (the mucous membrane) and moves outward (towards the connective tissue layer) as it spreads (see Figure 1).
It often goes undetected for many years, and in its later stages, this cancer is not easily treatable. Among those who develop esophageal cancer, their long-term survival rate is low, as it is estimated that only 12. 5% of patients live five years beyond the date of diagnosis (Triesschejin, Martijn 5).
The standard treatment option used to combat esophageal cancer is called an esophagectomy, in which the cancerous area of the esophagus is removed via surgery, however this procedure is very invasive, complicated, and is often times fatal. However, with today’s technological advancements, safer, less-invasive methods are beginning to replace this option and are proving to be successful in helping to extend the lives of those patients with severe esophageal cancer and aid in improving their quality of life.
One up-and-coming treatment option that is far more safe and practical than esophagectomy is the integration of lasers in photodynamic therapy, or PDT. Although it is still an experimental treatment, is ideal because it has no long-term side effects, is minimally invasive, can be done quickly with little recovery time, has the ability to precisely target the areas of the body where the cancer cells are present, and can be safely repeated multiple times until the desired results are achieved.
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Post-treatment, it has been known to cause sensitivity to light, particularly pertaining to the patient’s eyes and skin, however this has not been shown to be a significant issue among those treated with PDT. Photodynamic therapy uses special drugs, known as photosensitizing agents, along with laser light to kill cancer cells closer to the surface of the skin. The agents are injected into the body via and ‘switched on’ with light of the appropriate wavelength depending on the drug utilized. Chemical and molecular reactions within the ody from the drugs then destroy the cancer cells and work to rid the body of the esophageal disease. Although several sources of light are possibilities when performing photodynamic therapy, lasers are the most preferred. They are the most effective in emitting monochromatic light, or light that is of a single wavelength and color, corresponding to all of the different absorption maxima of photosensitizers’ compounds, and can be relatively easily coupled to optical fibers from 200 to 600 microns’ core sizes.
Specifically, the type of laser that is optimal for the treatment of esophageal cancer is a diode laser. These lasers are the most recent to be used in cancer treatment, and were developed just within the last fifteen years. Thus, they have higher quality beams, expanded ranges of wavelengths, and can be used on higher powers if desired. Diode lasers are ideal because they are simple to use, easy to transport, and do not require difficult installation like the gas (argon) and dye lasers used before them (Boucher 74).
The diode laser currently approved by the FDA is manufactured by Angiodynamics, and has been successfully used, along with the correct application of photosensitizers, in esophageal cancer treatments. “A good photosensitizer is preferably a pure compound with a constant composition” (Nyman 3).
And in esophageal cancer treatment via PDT, the best-proven photosensitizer is called porfimer sodium, also commercially known as Photofrin®.
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In fact, the United States’ Food and Drug Administration has only approved the use of this photosensitizer in the treatment of esophageal cancer via PDT (“Photodynamic Therapy” 2).
Porfimer sodium is injected intravenously, where it is then absorbed by all of the body’s cells, but only those cells that are normal and not cancerous are able to get rid of it. To allow for the body’s normal cells to rid themselves of the drug, two to three days are given between the drug’s administration and the activation of the drug by laser light.
After being passed down the throat through a small flexible tube called an endoscope, a thin fiber optic glass strand is used to direct the laser light at the affected area. The optical fiber is made of fused silica, and uses a balloon catheter to distribute a defined, controlled amount of light to the treated esophagus organ. If the beam were not diffuse, a direct beam (even at a low power) could be damaging to the esophageal tissue. The light is operated at weaker power of around 2 Watts to ensure that it does not burn any tissue, and it is relatively pain-free.
The treatment it is applied for no longer than an hour at a time and can often be done in an outpatient setting (reference all sources listed).
Normally, the most common wavelength used is red light, as its specific wavelength of 630 nanometers has been shown to work best when attempting to create the most effective and potent malignant cancer cell-killing method possible. Atomically speaking, following its activation by laser light, “…the photosensitizer is elevated from a ground state to a long lasting excited triplet state…. and it] can then react with cell membranes to form radical ions [intermediates] which interact further with oxygen to produce cytotoxic oxygenated molecules” (Gray 1).
More simply put, the excited photosensitizer activated by the laser light transfers its energy to other molecules before returning to its ground state, which generates a reactive oxygen species (intermediate) that is able to directly kill and destroy the esophageal tumor via oxidation, and later, indirectly, via inflammation.
Research has shown a huge increase in the survival rate of PDT patients receiving this treatment. Treated patients’ survival rates improved 25% over a span of five years compared to those who never received any type of treatment (Li 2).
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And although doctors have seen great success with the use of photodynamic therapy and diode laser treatments, there is still much more to be researched and improved upon. Currently, new drugs, such as Photochlor®, and others are being clinically tested to see if they can be used as photosensitizers in the treatment of esophageal cancer.
This photosensitizer looks promising, as it has already been shown to last a much shorter time and is more easily removed from the body than Photofrin® is. Also, scientists are looking at the possibility of using ointments containing ferrous or colbalt ions and hydrogen peroxide on the treated cancerous area to improve PDT outcomes along with laser light. And with the further advancement of technology, hopefully newer treatments will be able to not only improve the outcomes of patients with severe esophageal cancer, but be able to cure them of it once and for all.