Comparison of facial predilection sites for cutaneous squamous cell carcinoma and actinic keratosis in Japanese patients

Cutaneous squamous cell carcinoma (cSCC) and actinic keratosis (AK) occur most often on the face. Ultraviolet light is apparently their most common cause. As AK is considered to be a precursor of cSCC, their distribution on the face should be similar. However, cSCC often occurs on the temple or mandibular area, whereas AK arises on the central forehead, cheek or nose. We retrospectively evaluated differences in affected site distribution for cSCC (n = 54) and AK (n = 95). We found AK to occur preferentially on the central facial area (63/95, 66%), which is the most sun‐exposed area, and cSCC to occur preferentially on peripheral areas such as the temple and mandibular area (24/54, 44%). Those distributions were significantly different (P = 0.011, Fisher's exact test). This result suggests that cSCC occurs preferentially in the peripheral area compared with the central facial area, which further implies that either other factors are needed to make AK progress to cSCC in peripheral areas, or that peripheral cSCC can occur without preceding AK. This is the first report to focus on geographic assessment of cSCC and AK in detail. Further studies are needed to elucidate the mechanism of our finding.