Histologic subtype of treatment failures after noninvasive therapy for superficial basal cell carcinoma: An observational study

Background: There have been concerns that recurrences after noninvasive therapy for basal cell carcinoma (BCC) transform into a "more aggressive'' histologic subtype. Objective: We sought to evaluate the proportion of patients with a nonsuperficial treatment failure after noninvasive therapy for superficial BCC. Methods: An observational study was performed using data from a single blind, noninferiority, randomized controlled trial (March 2008-August 2010) with 5-year follow-up in patients with primary superficial BCC treated with methylaminolevulinate-photodynamic therapy, 5-fluorouracil, or imiquimod. Data were used from 166 adults with a histologically confirmed treatment failure. Results: A nonsuperficial subtype was found in 64 of 166 treatment failures (38.6%). Proportions with a more aggressive subtype than the primary tumor were 51.3% (38/74) for early and 28.3% (26/92) for later treatment failures (P = .003). The proportion of more aggressive early failures was significantly lower after imiquimod (26.3%) compared with methylaminolevulinate-photodynamic therapy (54.8%, P = .086) and 5-fluorouracil (66.7%, P = .011). Limitations: There was limited information on the exact time of occurrence of treatment failures. Conclusion: More aggressive treatment failure recurrences after noninvasive therapy for superficial BCC occur most often within the first 3 months posttreatment, probably indicating underdiagnosis of more aggressive components in the primary tumor rather than transformation.