Invasive squamous cell carcinoma after treatment of carcinoma in situ with 5% imiquimod cream.

Squamous cell carcinoma in situ has the potential to progress to invasive squamous cell carcinoma. This report presents two cases of punch biopsy-proven squamous cell carcinoma in situ, treated with once-daily application of 5% imiquimod cream for 6 weeks. Both patients developed moderate local inflammatory reactions during treatment. The first patient demonstrated clinical clearance of the scalp lesion after treatment. Two months later, he re-presented with a subcutaneous nodule at the same site. Histology was consistent with recurrent squamous cell carcinoma. Five months following excision of the recurrent tumour, he presented with metastatic squamous cell carcinoma to a cervical lymph node. The second patient had low-grade chronic lymphocytic leukaemia and presented with squamous cell carcinoma in situ of the leg that failed to clear clinically after treatment with imiquimod. He presented 4 months later with a focus of invasive squamous cell carcinoma within the lesion.