Long-term efficacy of photodynamic therapy with methyl aminolevulinate in treating Bowen's disease in clinical practice: a retrospective cohort study (2006-2017).

BACKGROUND: Photodynamic treatment with methyl aminolevulinate (MAL-PDT) is considered an effective and highly recommended treatment for Bowen's disease. However, its long-term efficacy remains to be established, as significant differences have been reported in this respect.

OBJECTIVE: The aim of the present study is to describe the results of a retrospective analysis of patients with Bowen's disease treated with MAL-PDT during the period 2006-17 at the Costa del Sol Hospital (Marbella, Spain).

MATERIAL AND METHODS: This study is based on a retrospective descriptive analysis of the clinical records of patients treated with MAL-PDT from June 2006 to September 2017. The analysis was based on calculating the mean and standard deviation values for the quantitative variables, and frequency distributions for the qualitative ones. The survival curves were plotted by the Kaplan-Meier method, and the log-rank test was used to assess differences in survival between groups. A cox regression analysis was performed to clarify the significant prognostic factors.

RESULTS: 537 tumours with histologically-confirmed Bowen's disease were treated with MAL-PDT. Recurrence-free survival at one year was 88%, and at five years, 71%. Tumour size >300 mm2 (≥21 mm in diameter p=0.019), its location in the upper extremities (p=0.029) and patient's age <70 years (p=0.028) were all associated with an increased risk of recurrence.

LIMITATIONS: Given the retrospective design of our study, the possible existence of information bias cannot be ruled out.

CONCLUSIONS: Although it is an appropriate treatment option for patients with Bowen's disease, MAL-PDT presents a risk of recurrence of almost 30% at five years. Larger lesions (>300 mm2 ; ≥21 mm in diameter) are more likely to recur than smaller ones. Therefore, appropriate selection is needed of the tumour to be treated, and prolonged follow-up should be provided. This article is protected by copyright. All rights reserved.