Traditional cancer treatments include surgery, chemotherapy, and radiation therapy. However, in recent years, photodynamic therapy (PDT) has emerged as a new alternative, along with immunotherapy and gene therapy.

Although still somewhat unfamiliar to many, the history of photodynamic therapy dates back a long time. It was scientifically established in the late 18th century, and in 1903, Danish physician Niels Finsen won the Nobel Prize for his carbon arc radiation therapy.

Photodynamic therapy expands beyond skin conditions to encompass a broader range of cancers, including head and neck, brain, lung, cervical, prostate, and breast. Active research is being conducted, Particularly in difficult-to-treat cancers such as pancreatic, peritoneal, and bile duct. I had the opportunity to meet with Kim Hyung-il, Director of the Photodynamic Therapy Research Center at Severance Hospital (Professor of Gastrointestinal Surgery), to learn more about it.

- What is photodynamic therapy?

Photodynamic therapy is a treatment method that utilizes light. It is often confused with laser therapy, but it is distinctly different. While both employ lasers, laser therapy acts only on the skin's surface and does not require additional substances.

On the other hand, photodynamic therapy requires three essential components: a light source, photosensitizers, and oxygen.

Photosensitizers are activated by exposing the appropriate wavelength and intensity of light, and they directly interact with tumors or generate reactive oxygen species to eradicate cancer.

The lasers used in photodynamic therapy do not generate heat, so patients do not feel any discomfort.

Photodynamic therapy has been actively used as a treatment method for skin cancer patients in various countries, including Eastern Europe and Brazil, for the past 30 to 40 years.

- I heard that the role of photosensitizers is crucial in photodynamic therapy.

Photosensitizers are derivatives of porphyrin compounds extracted from animal blood. When photosensitizers are intravenously injected, they quickly bind with LDL (low-density lipoprotein) in the blood and circulate throughout the body.

Tumors have a higher distribution of LDL receptors than normal tissues, allowing photosensitizers to accumulate in tumors for an extended period.

Moreover, the microvasculature around the tumor exhibits relatively high macrophage activity, resulting in a higher accumulation of photosensitizers compared to normal tissues. Subsequently, when lasers with absorption wavelengths specific to the photosensitizers are applied, the photosensitizers receive light from the light source, which blocks the formation of new blood vessels in the tumor and eliminates tumor cells.

In recent years, as minimally invasive treatments (such as laparoscopy, endoscopy, and thoracoscopy) have been applied, further active research is being conducted.

- Photodynamic therapy is gaining recognition as a new treatment option for advanced cancers.

For example, colorectal cancer has a 5-year survival rate of 93.9%, indicating a favorable prognosis.

However, the problem lies in "peritoneal carcinomatosis."

Peritoneal carcinomatosis is a condition where cancer cells have spread throughout the peritoneum, the membrane lining the abdominal cavity, with colorectal cancer being the primary cause.

When the abdomen is opened, the cancerous mass covers the entire peritoneum. In addition to visible tumors, numerous small cancer cells are present, along with very few blood vessels, resulting in a significant decrease in the effectiveness of chemotherapy.

In such cases, photodynamic therapy is considered the most effective treatment method. The photosensitizers used in photodynamic therapy are predicted to be highly efficient in peritoneal cancer, as they selectively bind to tumor cells.

This has been proven in a study on "Intraperitoneal PDT treatment effects in a peritoneal mouse model" conducted last year.

Although it was a non-clinical trial conducted before using photodynamic therapy in peritoneal cancer patients, it is anticipated to bring hope to patients with limited treatment options.

- How effective is photodynamic therapy for cholangiocarcinoma (bile duct cancer)?

Cholangiocarcinoma often exhibits late symptoms, and therefore, at the time of diagnosis, cancer has usually spread to major blood vessels and nerves around the liver.

Surgery is complicated in such cases, and options such as biliary drainage and bypass via endoscopy can only relieve symptoms.

In this context, photodynamic therapy serves as an alternative treatment.

The bile duct provides an ideal environment for photodynamic therapy as it allows light to travel directly in a straight line from the liver, where bile is produced, to the duodenum.

After treatment, a stent is inserted into the bile duct to prevent the re-growth of cancerous tissue and blockage of the duct.

Photodynamic therapy for cholangiocarcinoma not only locally eliminates cancer but also improves jaundice and inhibits cancer progression. Significant results have recently been achieved in pancreatic cancer beyond cholangiocarcinoma.

- What are the possible side effects of photodynamic therapy?

There are only mild, controllable side effects associated with photodynamic therapy.

The systemic side effects caused by photosensitizers may lead to skin photosensitivity, and patients may exhibit skin hypersensitivity reactions to almost all light sources after photosensitizer administration.

However, the risk is shallow by following simple guidelines regarding light exposure.

- What are the major advantages of photodynamic therapy?

Since photodynamic therapy has been conducted on a few patients, research has been relatively slow compared to surgical treatments, which have been predominant.

However, recent medical trends have been focused on "minimally invasive surgery" that reduces the patient's recovery period and improves their quality of life, as well as "targeted therapy" that selectively kills cancer cells.

In this context, photodynamic therapy is a suitable treatment method.

Furthermore, recent advancements in diagnostic techniques and the development of new photosensitizers have made it possible to expect complete remission in specific conditions.

Most importantly, photodynamic therapy has the advantage of being a simple procedure that can be combined with other treatment methods. We will strive to accelerate research for its commercialization shortly.