Chronological changes in trichofolliculoma: Folliculosebaceous cystic hamartoma is not a very-late-stage trichofolliculoma.

Some authors have reported that the secondary hair follicles in trichofolliculomas (TF) undergo regressive changes and are subsequently replaced by the developed sebaceous elements, and that folliculosebaceous cystic hamartoma (FSCH) is a TF at a very late stage. In the present study, we revaluated the histopathological features of 40 TF lesions, focusing on their chronological changes. The results of the present study indicate that while the secondary follicles in the TF exhibited the hair cycle, the normal hair cycle was out of control, and tertiary hair follicles randomly developed from the involuting secondary follicles. The repeated development of hair follicles in this disordered hair cycle caused the development of chains of several continuous hair follicles in late-stage TF. In the TF lesions, no features indicating the replacement of the regressing secondary hair follicles by any sebaceous elements were observed, thereby suggesting that FSCH is not a very-late-stage TF.

Keratoacanthoma en plaque/nodule: A brief report of the clinicopathological features of five cases.

Keratoacanthoma (KA) is characterized by exoendophytic growth with a central keratin-filled crater, representing the crateriform architecture. We herein report five rare cases of KA without a central keratin-filled crater. These KA cases histopathologically showed that one or a few infundibular structures/isthmic lobules had their own open keratotic pores on the surface without a common merged keratotic plug/horn, clinically representing verrucous (keratotic) plaque/nodule, namely, "KA en plaque/nodule". KA rarely but on occasion does show verrucous plaque (or nodular) lesions without a central keratin-filled crater, as the notion that KA invariably shows crateriform architecture is nonsensical.

Focus of tricholemmal differentiation (tricholemmal carcinoma) within Bowen's disease/carcinoma.

Bowen's disease (BD)/carcinoma is a type of squamous cell carcinoma of the skin, however, the possibility of adnexal differentiation (the development of sebaceous carcinoma or porocarcinoma) occurring in BD/carcinoma has been suggested. We herein describe a case of BD with superficial invasive carcinoma, which showed a clear cell focus, demonstrating tricholemmal differentiation. This clear cell focus showed the following findings: primarily composed of clear cells, somewhat columnar clear cells aligned in a palisade along a discernible basement membrane, tricholemmal keratinization and glycogen contained within the cells. In addition, the immunohistochemical profile in this clear cell focus, namely, negative staining for cytokeratin (CK)1 and positive staining for CK17 and calretinin in the inner cells of the neoplastic lobule, corresponded to that of the outer root sheath cells. This case suggested that adnexal differentiation can rarely occur within true BD/carcinoma, although adnexal carcinomas are commonly associated with a simple bowenoid change.