Neoplasms of small adnexal keratinocytes: new developments new questions

摘要

The exact nature of human BCC has been a source of controversy for many years. Many pathologists have believed it to be adnexal rather than epidermal and derived from multipotential keratinocytes similar to those in the embryonal anlagen of folliculosebaceous-apocrine units. Over the last 20 years, as primitive follicular neoplasms became better characterized, entities such as desmoplastic trichoepithelioma and trichoblastoma could be culled from the overly-inclusive category "basal cell carcinoma". Within the last 4 years, as more and more individual keratin markers become available, multiple studies have shown that BCC have virtually identical cytokeratin profiles to both trichoepithelioma and trichoblastoma. These profiles point to follicular outer root sheath, possibly the bulge region, as the common differentation pathway of the three tumor groups. Certain non-keratin immunohistochemical markers, usually indicators of malignancy in general, aid in distinguishing human BCC from benign small cell follicular neoplasms. Does this mean that all BCC's are really primitive follicular carcinomas? Trichoepithelioma and trichoblastoma categories in human dermatopathology have become muddied, with different authors using one of the terms preferentially to describe lesions in both groups. Should we re-lump all of them, as Ackerman proposes, into a large category "Trichoblastoma" with the main subdivisions "benign" and "malignant"?