Differentiating keratoacanthoma from squamous cell carcinoma-In quest of the holy grail.

To distinguish keratoacanthomas from squamous cell carcinomas remains a diagnostic challenge in dermatopathology. Several immunohistochemical and cytogenetic markers have been evaluated; however, so far there has been no unequivocal evidence supporting practical application of any of these markers. Recent studies have evaluated the composition of tumor-associated immune infiltrate, in particular the number and distribution of CD123-positive plasmacytoid dendritic cells in making this distinction; but these cells also do not appear to be a consistent biomarker in distinguishing keratoacanthoma from squamous cell carcinoma.