Photodynamic therapy vs. topical imiquimod for treatment of superficial basal cell carcinoma: a subgroup analysis within a noninferiority randomized controlled trial

Background A recent noninferiority randomized controlled trial (RCT) indicated that imiquimod can be considered as superior to methylaminolevulinate photodynamic therapy (MAL-PDT) in the treatment of superficial basal cell carcinoma (sBCC). Knowledge of treatment effectiveness in subgroups of patients is of great value in clinical practice to select the most effective treatment for an individual patient with sBCC. Objectives To explore whether the relative treatment effect of MAL-PDT and imiquimod is consistent across subgroups defined by patient and tumour characteristics. Methods Data were derived from a single-blinded, noninferiority, multicentre RCT comparing MAL-PDT, topical imiquimod and fluorouracil (ISRCTN79701845). Treatment success was defined as free of tumour recurrence at 12-month follow-up. Subgroup analyses were performed for subgroups defined by sex, age, tumour location and tumour size. Results Two hundred and two patients received MAL-PDT and 198 received imiquimod. The superiority of imiquimod vs. MAL-PDT was observed in subgroups of females, sBCC on the trunk and large tumours with risk differences in favour of imiquimod of 18.4% [95% confidence interval (CI) 7.8-29.0%], 21.0% (95% CI 10.9-31.1%) and 18.9% (95% CI 7.1-30.7%), respectively. Higher probability of treatment success for imiquimod vs. MAL-PDT was consistently found in all other subgroups with the exception of sBCC localized on the lower extremities in older patients. In the latter subgroup, the risk difference at the expense of imiquimod was -57.3% (95% CI -81.7% to -32.9%). Conclusions Imiquimod remains the first-choice treatment for sBCC in terms of effectiveness. In older patients with sBCC on the lower extremities MAL-PDT might be preferred. Results should be interpreted carefully as subgroup analyses were exploratory and not driven by prior hypotheses.