Topical Treatment of Cutaneous Squamous Cell Carcinoma in Situ and the Impact of Clinical Risk Factors and Positive Histologic Margins at the Time of Diagnosis

Limited data exist for the efficacy of topical 5-fluorouracil (5-FU) and imiquimod for cutaneous squamous cell carcinoma (cSCC) in situ (cSCCis) with positive histologic margins at the time of diagnosis. Identify the efficacy of topical 5-FU and imiquimod in the treatment of cSCCis with positive histologic margins at the time of diagnosis in relation to clinical risk factors. Pathology records were screened at a single institution from 2014 to 2021 for cSCCis with positive histologic margins. Patients were included if they were treated with curative intent with topical 5-FU or imiquimod. Recurrences were evaluated in relation to multiple clinical risk factors. Of 215 patients treated with 5-FU or imiquimod after biopsy-proven cSCCis, 19 patients had recurrent cSCCis and 1 patient had upstaging to invasive cSCC. Recurrence was more likely in larger lesions at the time of initial biopsy ( p = .033) and in patients treated with topical imiquimod compared with topical 5-FU ( p < .01). Topical 5-FU is an appropriate therapy for cSCCis in the correct clinical scenario. Extra consideration should be taken for use of 5-FU in larger diameter cSCCis lesions. Although limited by sample size, our study does not support the use of imiquimod for cSCCis.