Abstract: The primary outcome measures were complete clearance of lesions after the first treatment cycle and recurrence rate at 12 months. Our secondary outcomes included the number of lesions that cleared after each treatment cycle, the number of treatment cycles needed to achieve clearance, the recurrence rates at > 12 months, cosmetic outcome, quality of life assessment, and adverse outcomes as reported by both participant and clinician. We included 9 studies, with a total of 363 participants. One study demonstrated statistically significantly greater clearance of lesions of Bowen's disease with MAL-PDT (methyl aminolevulinate with photodynamic therapy) when compared with placebo-PDT (RR (risk ratio) 1.68, 95% CI (confidence interval) 1.12 to 2.52; n = 148) or cryotherapy (RR 1.17, 95% CI 1.01 to 1.37; n = 215), but there was no significant difference when MAL-PDT was compared to 5-FU (5-fluorouracil). One study demonstrated statistically significantly greater clearance of lesions with ALA-PDT (5-aminolevulinic acid with photodynamic therapy) versus 5-FU (RR 1.83, 95% CI 1.10 to 3.06; n = 66), but no statistically significant difference in recurrence rates at 12 months (RR 0.33, 95% CI 0.07 to 1.53). Cryotherapy showed no statistically significant difference in clearance rates (RR 0.99, 95% CI 0.78 to 1.26) or recurrences at 1 year (RR 1.48, 95% CI 0.53 to 4.17) when compared to 5-FU in 1 study of 127 participants. One study compared imiquimod to placebo and demonstrated statistically significantly greater clearance rates in the imiquimod group (9/15 lesions) compared to placebo (0/16) (Fisher's Exact P value < 0.001). The imiquimod group did not report any recurrences at 12 months, but at 18 months, 2/16 participants in the placebo group had developed early invasive squamous cell carcinoma. Overall, there has been very little good-quality research on treatments for Bowen's disease. There is limited evidence from single studies to suggest MAL-PDT is an effective treatment. Although cosmetic outcomes appear favourable with PDT, five-year follow-up data are needed. Significantly more lesions cleared with MAL-PDT compared to cryotherapy. No significant difference in clearance was seen when MAL-PDT was compared with 5-FU, but one study found a significant difference in clearance in favour of ALA-PDT when compared to 5-FU. There was no significant difference in clearance when cryotherapy was compared to 5-FU. The lack of quality data for surgery and topical cream therapies has limited the scope of this review to one largely about PDT studies. The age group, number, and size of lesions and site(s) affected may all influence therapeutic choice; however, there was not enough evidence available to provide guidance on this. More studies are required in the immunosuppressed populations as different therapeutic options may be preferable. Specific recommendations cannot be made from the data in this review, so we cannot give firm conclusions about the comparative effectiveness of treatments.

Plain-language summary: We included 9 randomised controlled trials, with a total of 363 participants. No studies examined surgical methods. Photodynamic therapy appears to be an effective treatment and has the benefit of minimal scarring compared with cryotherapy or 5-fluorouracil. Cryotherapy is convenient and less expensive, but does not appear to be as effective as photodynamic therapy and results in more scarring; 5-aminolevulinic acid with photodynamic therapy (ALA-PDT) appears to be more effective than 5-fluorouracil, whereas methyl aminolevulinate with photodynamic therapy (MAL-PDT) does not appear to be as good as 5-fluorouracil. One study demonstrated benefit with imiquimod cream. Specific recommendations cannot be made from these data, so this review cannot give firm conclusions about the comparative effectiveness of treatments. There is a clear need for future research to focus on a range of different studies comparing various therapies with each other, and in particular to surgical treatments to provide high-quality evidence to guide clinical practice. The age group, number and size of lesions, sites affected, and immunological status may all influence therapeutic choices. Longer-term follow up (up to 10 years) is needed to determine the effect of treatments on risk of progression of lesions of Bowen's disease to squamous cell carcinoma.