Methylaminolaevulinate-based photodynamic therapy of Bowen's disease and squamous cell carcinoma

Background: Photodynamic therapy (PDT) with methylaminolaevulinate (MAL) is an approved noninvasive treatment option for actinic keratosis and Bowen's disease (BD), two precursors of invasive squamous cell carcinoma (SCC). Objectives: To assess efficacy, prognostic features, tolerability and cosmetic outcome of MAL-PDT for the treatment of BD and SCC. Methods: In total, 112 biopsy-proven lesions of BD and SCC in 55 subjects were treated in an outpatient setting. MAL cream (160 mg g^-1) was applied for 3 h prior to illumination with a light-emitting diode source (wavelength range 635 ± 18 nm; light dose 37 J cm^-2). A second MAL-PDT session was given 7 days later. Complete response rate at 3 months after the last treatment, recurrence rate at the 24-month follow-up, and cosmetic outcome were recorded. Results: The overall complete response rates were 73.2% at 3 months and 53.6% at 2 years. Clinical thickness, atypia and lesion depth were significant predictors of the response at 3 months when using a univariate analysis (P <0.001). A multivariate logistic regression model, with robust variance estimation, showed that cell atypia was the only statistically significant independent predictor of the treatment outcome at 3 months. Conclusions: MAL-PDT may represent a valuable, effective and well tolerated treatment option with good cosmetic outcome for superficial, well-differentiated (Broders' scores I and II) BD and microinvasive SCC. In contrast, its use for superficial SCCs with a microinvasive histological pattern and for nodular, invasive lesions, particularly if poorly differentiated keratinocytes are present (Broders' scores III and IV), should be avoided.