C

Acanthosis is defined histologically as diffuse epidermal hyper-plasia caused by thickening of the prickle-cell (stratum spinosum) layer of the epithelium, not of the superficial cornified layer or the basal lamina and without implying increased mitoses per se [Shingaki, 2010, PMID 20500798; Kapoor, 2010, PMID 21137622].