Photodynamic Therapy (PDT) — How It Works, Benefits & Recovery — Procedure Guide, Recovery & Risks | MyMedicPlus

Photodynamic therapy (PDT) is a targeted cancer and pre-cancer treatment combining a photosensitiser drug (a light-activated chemical) with controlled exposure to specific wavelength light to generate cytotoxic reactive oxygen species (singlet oxygen, free radicals) that selectively destroy abnormal cells. PDT exploits the preferential uptake and retention of photosensitiser agents by abnormal, rapidly proliferating cells relative to surrounding healthy tissue. When the photosensitiser is activated by light of the appropriate wavelength, it undergoes a photochemical reaction transferring energy to molecular oxygen — producing singlet oxygen that oxidises and damages cellular membranes, mitochondria, and DNA, triggering cell death by apoptosis and necrosis, and occluding tumour vasculature. In dermatology, the most widely used form is topical PDT using 5-aminolaevulinic acid (5-ALA, e.g. Ameluz) or its methyl ester (methyl aminolaevulinate, MAL, e.g. Metvix) applied to the skin lesion, which is metabolised intracellularly to the photosensitiser protoporphyrin IX (PpIX). Illumination with red light (630–635 nm) or daylight (daylight PDT) activates PpIX. Systemic PDT uses intravenously administered porfimer sodium (Photofrin) or temoporfin (Foscan) and fibre-optic light delivery for internal tumours (oesophageal, lung, bile duct cancers; Barrett's oesophagus with high-grade dysplasia).

Topical PDT is NICE-approved and guideline-recommended for: actinic keratoses (solar keratoses) — the most common indication, achieving superior cosmetic outcomes and field treatment versus cryotherapy; Bowen's disease (squamous cell carcinoma in situ) — 85–90% complete response at 3 months; superficial basal cell carcinoma (sBCC) — 85–90% complete response, particularly for lesions on cosmetically sensitive sites (face) where excision scars are undesirable; and nodular BCC less than 2 mm depth. The British Association of Dermatologists (BAD) and NICE guidelines (NG12, TA155) support PDT as a first-line option for these conditions. PDT is particularly advantageous for multiple lesions at the same anatomical site (field treatment — treating an entire sun-damaged skin area rather than individual lesions), lesions at sites with poor wound healing potential (lower leg), and patients with multiple BCCs or widespread actinic keratoses. Systemic PDT indications include: superficial oesophageal cancer and palliation of obstructing oesophageal squamous carcinoma; endobronchial lung cancer (central type); Barrett's oesophagus with high-grade dysplasia as an alternative to thermal ablation (radiofrequency ablation now preferred at most centres); cholangiocarcinoma palliation; and bladder cancer. PDT is not suitable for thick, deeply invasive cancers (>2 mm for skin PDT) or conditions requiring systemic anti-cancer therapy.

Topical skin PDT procedure: (1) Lesion preparation — scale and crust are removed from the target lesion(s) by curettage or gentle abrasion to improve photosensitiser penetration. (2) Photosensitiser application — a 1–2 mm layer of 5-ALA or MAL cream is applied to the lesion with a 5–10 mm margin of surrounding skin, covered with an occlusive dressing. (3) Incubation — the cream is left in contact with the skin for 3 hours (MAL, conventional PDT) or in daylight (daylight PDT, where the photosensitiser is activated by ambient daylight immediately after application without a dark incubation phase). (4) Illumination — the dressing is removed and the cream wiped off. A red light source (LED lamp, 630 nm) delivers the prescribed light dose (typically 37–75 J/cm², calibrated by the lamp's irradiance and illumination time). Daylight PDT is performed outdoors on a clear day for 2 hours. Cooling spray or a fan reduces the stinging and burning sensation experienced during illumination. Treatment time is 7–15 minutes per lesion with conventional PDT. Multiple lesions can be treated simultaneously. A second PDT session 1–2 weeks after the first significantly improves complete response rates for BCC and Bowen's disease. Systemic PDT for oesophageal or lung tumours involves IV porfimer sodium (2 mg/kg) 48 hours before endoscopic fibre-optic laser (630 nm) illumination of the tumour under sedation.

Topical PDT achieves 85–90% complete histological clearance rates for superficial BCC and Bowen's disease at 3 months — equivalent to surgical excision for superficial lesions, but with markedly superior cosmetic outcomes (minimal scarring, excellent skin texture and colour preservation) because healthy tissue is largely spared. For actinic keratoses, 3-month clearance rates of 85–95% are documented in randomised trials including the KERAFLEX and Nevisense studies; field-directed PDT reduces the risk of progression to invasive squamous cell carcinoma. Patient satisfaction with the cosmetic result of PDT exceeds 90% in large dermatology clinic series, particularly for facial lesions where scarring from surgical excision would be cosmetically significant. Recurrence rates at 5 years are 15–20% for superficial BCC (comparable to non-melanoma skin cancer recurrence rates from cryotherapy, and better than from non-specialist surgical excision). Daylight PDT is equally effective as conventional lamp PDT for actinic keratoses and Bowen's disease with reduced procedure time and substantially less treatment-site pain (stinging/burning during illumination is the main limiting factor of conventional PDT). For systemic PDT in palliation of obstructing oesophageal cancer, dysphagia improvement is achieved in 70–85% of patients.

Topical PDT side effects are predominantly local and temporary. Stinging, burning, and erythema during light illumination are the main treatment-limiting factors for conventional lamp PDT — experienced by 80–90% of patients, typically rated as moderate (4–6/10 pain scale); these resolve within hours of treatment. Post-treatment erythema (redness), oedema (swelling), crusting, and scaling of the treatment site persist for 2–6 weeks during healing. Localised infection (bacterial or impetigo) at the treatment site affects 2–5% and requires topical or oral antibiotic treatment. Hyperpigmentation or hypopigmentation at treated sites occurs in 5–15%, more common in skin types IV–VI; usually resolves over 3–6 months. Post-inflammatory changes from the inflammatory wound healing process are expected and are part of the mechanism of clearance. Photosensitivity to bright light at treated sites persists for 24–48 hours post-treatment (topical PDT); patients must avoid direct sun exposure to treated areas during this window. Systemic PDT with porfimer sodium causes prolonged (4–6 weeks) generalised photosensitivity — patients must avoid sun and bright indoor light and wear protective clothing during this period. PDT is not associated with systemic immunosuppression and does not increase susceptibility to infections or secondary malignancies.

After topical PDT, patients return home immediately. The treated skin is red, swollen, and may be crusted — resembling a moderate sunburn. A simple non-adherent dressing (Mepilex Lite, Mepitel One, or petroleum gauze) protects the area for 1–2 weeks during the desquamation (peeling) phase. Facial lesion patients are advised of likely visible skin changes for 2–3 weeks. Emollient moisturiser (Doublebase, Diprobase, or equivalent) soothes treated skin and promotes healing. Mild analgesics (paracetamol, ibuprofen) manage any residual discomfort. Sun avoidance to treated areas for 48 hours (topical PDT) or 4–6 weeks (systemic PDT) is mandatory. No downtime is required — most patients with facial PDT choose 1–2 weeks of social downtime to avoid visible skin changes. Complete healing and assessment of treatment response is at 3 months, when the dermatologist inspects for residual lesion and performs dermoscopy or biopsy if needed. A second PDT course may be offered for incomplete responses. Surveillance for new skin cancers continues with regular annual dermatology review for patients with a history of multiple non-melanoma skin cancers.