Photodynamic therapy (PDT) is a localized cancer treatment that utilizes a two-step process to selectively destroy cancer cells while minimizing damage to healthy tissue.
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How PDT Treats Cancer
The effectiveness of PDT against cancer stems from a photochemical reaction that is triggered only in the target area. The process involves:
Photosensitizer Administration: A light-sensitive drug, called a photosensitizer, is administered to the patient.
This can be done intravenously, topically (as a cream or gel), or orally, depending on the location of the tumor. Cancerous and precancerous cells are known to absorb and retain these photosensitizers more effectively and for a longer duration than healthy cells. Light Activation: After a specific waiting period (from minutes to several days), a light of a particular wavelength is shined on the cancer site.
This light is harmless on its own, but when it reaches the photosensitizer that has accumulated in the tumor cells, it "activates" the drug. Cell Death: The activated photosensitizer reacts with oxygen present in the cells, producing highly toxic reactive oxygen species (ROS), such as singlet oxygen.
These ROS cause direct damage to the cancer cells, leading to their death through a process called apoptosis (programmed cell death) or necrosis (uncontrolled cell death).
In addition to directly killing cancer cells, PDT may also work in other ways to combat tumors:
Vascular Damage: The photosensitizer can also accumulate in the blood vessels that supply the tumor. When the light activates the drug, it can damage these vessels, cutting off the blood, oxygen, and nutrients the tumor needs to survive.
Immune System Activation: The process of PDT can also trigger a localized and systemic immune response, prompting the body's own immune system to recognize and attack the remaining cancer cells.
Types of Cancer Treated with PDT
PDT is most effective for treating cancers that are on or just beneath the skin, or on the lining of internal organs that can be reached with a light source, typically delivered via an endoscope.
Skin Cancers: Superficial basal cell carcinoma, squamous cell carcinoma in situ (Bowen's disease), and actinic keratosis (precancerous skin patches).
Esophageal Cancer: Early-stage esophageal cancer and Barrett's esophagus (a precancerous condition).
Lung Cancer: Early-stage non-small cell lung cancer and for palliative care to clear airways blocked by tumors.
Head and Neck Cancers: Certain cancers of the head and neck.
Pancreatic Cancer: Used as a localized treatment option.
Bile Duct Cancer (Cholangiocarcinoma): Used to treat tumors in the bile duct.
Side Effects and Limitations
While PDT is a well-tolerated treatment, some side effects are associated with it:
Photosensitivity: This is the most common side effect. The photosensitizing drug makes the skin and eyes extremely sensitive to all forms of light, including sunlight and bright indoor lights, for a period that can last from several weeks to a few months.
Patients are advised to take strict precautions to protect themselves from light exposure during this time. Localized Side Effects: Depending on the treatment site, patients may experience burning, stinging, redness, swelling, and blistering.
These are typically temporary and resolve as the treated area heals. Other Side Effects: For treatments in internal organs like the esophagus or lungs, patients may experience symptoms like difficulty swallowing, stomach pain, or a cough.
PDT has some limitations.
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