S3C22aP10a-3: In this field, the features of a lichen planus-like lichenoid reaction are represented. In the epithelium, there are lytic defects containing apoptotic debris at the dermal-epidermal interface. The inflammatory infiltrates are composed of lymphocytes with a high component of migratory histiocytes. Some of the histiocytes have migrated into the epithelium. The epithelium is composed of hypertrophied keratinocytes with abundant acidophilic cytoplasm, plump nuclei, and prominent nucleoli. Granular cells are prominent; they contain large, keratohyaline granules. There is piecemeal representation of a basal unit; in this unit, the epithelial cells have lavender cytoplasm, a quality that equates with regenerative activity.

S3C22aP10a-4: The erosive changes at the dermal-epidermal interface define the process as a lichenoid process; the target cells are basal keratinocytes. A basal unit, as such, is not represented; either it has been destroyed by the erosive process, or the cells, of what was the basal unit, have made a phenotypic transformation and entered the pathway of terminal differentiation. In the latter event, the cells of the basal unit would have assumed a defensive phenotype from which the formation of an impervious barrier at the surface is promoted. The superficial unit is hypertrophied - a characteristic feature of lichenoid reactions of lichen planus-like type. The changes in the superficial unit are also basic for the reaction seen in established lichenoid reactions.