Dilute Intralesional 5-Fluorouracil for the Treatment of Squamous Cell Carcinomas and Keratoacanthomas: A Case Series

Intralesional 5-fluorouracil (5-FU) is a promising, yet sparsely studied alternative to surgical treatment for nonmelanoma skin cancer (NMSC).¹ While intralesional 5-FU is not a Food and Drug Administration (FDA)-approved treatment for NMSC, it has been reported as a non-surgical option in patients who decline or are ineligible for surgery. Previous studies of intralesional 5-FU have reported concentrations ranging from 30 to 50 mg/mL.^1-3 We report the use of dilute intralesional 5-FU 10.0 mg/mL and 16.7 mg/mL. The purpose of this retrospective study is to determine the clinical clearance rate of dilute intralesional 5-FU therapy at a single institution.

Historical billing data were searched to identify all patients who received intralesional chemotherapy at Dartmouth-Hitchcock Medical Center from July 1, 2008 to July 1, 2018. The resulting records were manually reviewed to identify cases in which intralesional 5-FU was used for cutaneous squamous cell carcinoma (cSCC) and keratoacanthoma (KA). Included lesions consisted of both histopathologically proven and clinically diagnosed tumors. All dilutions were prepared using 5-FU 50 mg/mL standard injection solution. Treatment efficacy was determined by clinical observation of complete tumor clearance as documented in clinical notes. Treatment failure was defined as tumor persistence warranting discontinuation of intralesional 5-FU and initiation of alternative therapy. Cases were excluded if the patient was lost to follow-up while intralesional 5-FU therapy was ongoing.

We identified 11 patients who received dilute intralesional 5-FU chemotherapy for 40 cSCCs and 10 KAs. These cases are summarized in Table 1. The patients were non-Hispanic white and predominantly female (7/11), with an average age of 69 at the time of treatment initiation. On average, each patient