We read with interest the results of the randomised controlled trial by Arits and colleagues,1
in which they reported that topical fluorouracil was not inferior to, and imiquimod was superior to, methyl aminolevulinate photodynamic therapy (MAL-PDT) in terms of treatment success of superficial basal-cell carcinoma after 1 year of follow-up. From their results, they conclude that topical imiquimod should be considered the first choice treatment for superficial basal-cell carcinoma.
The authors mention in the discussion that the proportion of successfully treated patients was lower than expected for MAL-PDT, which is not in agreement with previously published studies reporting higher success rates of photodynamic therapy in superficial basal-cell carcinoma.2
To provide an explanation for the latter discrepancy, they suggest that the repetitive photodynamic therapy courses used in previous studies might explain the higher response rates.
However, the authors fail to mention a crucial clinical, but also histopathological, parameter that strongly affects the efficacy of photodynamic therapy—namely, the presence of pigmentation. Pigmented superficial basal-cell carcinomas are well known to respond poorly to photodynamic therapy, since the pigment has a competitive role in light absorption, resulting in very low therapeutic effects.3
Based on this observation, in a recent review article releasing guidelines for the practical use of MAL-PDT in non-melanoma skin cancer, the guidelines clearly state that the method is not suitable for treatment of pigmented lesions, which is also a common practice among dermatologists dealing with dermato-oncology.4
As described in the methods section of Arits and colleagues' study, patients with clinically or histologically pigmented lesions were not excluded. Since participants were pooled and treated in a randomised manner, a proportion of pigmented superficial basal-cell carcinomas were treated with photodynamic therapy, which may provide an additional explanation for the lower response rate in the latter subgroup. This theory would be elucidated further if the investigators provided clinical and histological data for the rate of pigmented lesions set under treatment with photodynamic therapy, to clarify whether this parameter is responsible for the treatment failure in some cases. If so, the latter should be also viewed as an additional possible explanation of the lower response rates in the group of superficial basal-cell carcinomas treated with photodynamic therapy.
Therefore, it would be very interesting if the authors provided the response rates of non-pigmented basal cell carcinomas in the three groups of their study.
We declare that we have no conflicts of interest.