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

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).

To assess efficacy, prognostic features, tolerability and cosmetic outcome of MAL-PDT for the treatment of BD and SCC.

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.

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.

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.