2013 Volume 123 Issue 9 Pages 1775-1784
We examined the histopathological diagnosis of 1,527 patients that had been clinically diagnosed with keratoacanthoma (KA) at Sapporo Dermatopathology Institute. Of these 1,527 patients, 873 were male, 650 were female, and 4 were of unknown gender. Those lesions were most frequently located on the face (in about two thirds of cases). In 999 patients (65.4%), the histopathological architecture of KA was observed (KA lesion). The mean age at resection of KA lesion (68.3±15.1 years old) was significantly higher in these patients than in patients without KA histopathological architecture (non-KA lesion) (61.0±20.5 years old). In sun-exposed areas, the rate of KA lesions was high; 28.5% of the patients had malignant neoplasms. Notably, in patients over 60 years old, 39.0% of cases were malignant. The rate of malignant lesions was highest in sun-exposed areas in elderly patients. The mean age at resection of malignant lesions (77.5±11.5 years old) was significantly higher than for benign lesions (61.1±17.3 years old). The 1,527 cases included 1,397 (85.9%) epithelial tumors, 99 (8.5%) non-epithelial tumors, and 31 (2.0%) inflammatory lesions. Based on our finding, lesions clinically suspected as KA should be totally resected as soon as possible, especially on the faces of elderly patients.