Metastatic cutaneous squamous cell carcinoma derived from actinic keratosis

BACKGROUND. Squamous cell carcinoma (SCC) with histologically contiguous actinic keratosis has long been thought of as a tumor with minimal risk for metastasis. The objective of this study was to determine if contiguous actinic keratosis is present in the original tumors of metastatic cutaneous SCC and to describe the histologic features of these tumors. METHODS. The primary lesions of 22 patients with metastatic cutaneous SCC were examined using light microscopy. RESULTS. Contiguous actinic keratosis was present histologically in 44% of the original lesions of cutaneous SCC that metastasized. The average tumor thickness was 6.6 mm. Greater than 66% of the tumors were well or moderately differentiated. The skin adjacent to the tumors showed solar degeneration in almost all instances. CONCLUSIONS. The histologic presence of contiguous actinic keratosis is not a useful predictor of the metastatic behavior of cutaneous SCC. Increased tumor thickness and depth of invasion are the most consistent histopathologic features of cutaneous SCC that metastasize.