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Photodynamic therapy

Therapia photodynamica

Photodynamic therapy (PDT) is a method of local treatment for tumor tissues that combines the administration of a specific chemical agent with its subsequent activation by light. This approach triggers a cascade of reactions that are destructive to pathological cells and is used in both palliative and second-line treatment regimens.

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PhotosensitizerTherapeutic chemical agent (ATC code: L01XD)
AccumulationRelatively selective in pathological tissue
ActivationCarried out using laser radiation
Level of evidenceStrength of recommendation grade – C (reliability – 4)
2 min readFor medical studentsUpdated 10.10.2026
Material prepared by WhiteCoat Pro editorial team based on platform study guidesPending instructor review

Mechanism of action

The process of photodynamic therapy is a strict sequence of steps leading to the targeted destruction of the pathological lesion:

  1. Drug administration. The patient is administered a specialized chemical agent — a photosensitizer.
  2. Tissue accumulation. There is a relatively selective (not absolute and not systemic) accumulation of the administered drug directly within the tumor-affected tissues.
  3. Light activation. The photosensitizer accumulated in the cells is activated using targeted light exposure (laser).
  4. Photodynamic effect. Activation triggers a complex cascade of intracellular biochemical reactions.
  5. Cell death. The ultimate result of the triggered cascade is the inevitable death of tumor cells.

Palliative care for biliary tract lesions

In biliary surgery, the method is used in the format of intraductal PDT. The main focus of such treatment is palliative care for severe patients.

Indications for the procedure:

  • Localized intraductal lesion of the biliary tract.
  • Periductal infiltrative growth pattern of the tumor.
  • Locally advanced process: stages IIIa–IVa, which corresponds to the T3–4 N0 M0 classification.

Clinical goals:

  • Restoration and improvement of adequate bile drainage.
  • General improvement in the quality of life of the inoperable patient.
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Application in non-muscle-invasive bladder cancer

In non-muscle-invasive bladder cancer (NMIBC), photodynamic therapy has the status of a 2nd-line treatment option. It is used in cases where previous conservative or surgical treatment has proven ineffective.

Methodology features:

  • The photosensitizer is administered intravenously.
  • The mucous membrane of the bladder is targeted with laser irradiation.

Clinical significance and perspectives: A number of clinical studies strongly indicate that the use of PDT helps reduce the number of disease relapses. Currently, the method continues to evolve: the medical community is actively refining optimal regimens and accumulating statistical data.

Final treatment parameters are strictly individual and depend on:

  • The extent of the tumor process along the mucous membrane.
  • The pharmacological properties of the photosensitizer used.
  • The chosen dose of laser radiation.
How to memorize

Five steps of PDT: Administered (drug) — Accumulated (selectively) — Irradiated (with laser) — Triggered (effect) — Destroyed (tumor).

Class and exam questions

How selectively does the photosensitizer accumulate in the tumor?

Drug accumulation is relatively selective: it predominantly lingers in pathological tissue, but does not possess absolute specificity.

At which stages of bile duct lesions is PDT indicated?

The method is indicated for stages IIIa–IVa (according to the TNM system, this is T3–4 N0 M0) when palliative improvement of bile drainage is required.

As what line of therapy is PDT used in bladder cancer?

PDT is recommended strictly as a 2nd-line treatment option upon confirmed ineffectiveness of prior treatment for non-muscle-invasive cancer.

What do doses and treatment regimens depend on during bladder treatment?

Parameters depend on the extent of the tumor along the mucosa, the nature of the administered drug, and the chosen dose of laser radiation.

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What else to study on this topic

  • Types and generations of photosensitizers (ATC code L01XD)
  • Biophysics of the photodynamic effect and intracellular cascades
  • Quality of life assessment in palliative biliary drainage
  • Criteria for failure of 1st-line therapy in non-muscle-invasive bladder cancer
  • Calculation of laser radiation dose depending on the area of mucosal lesion

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