title: Epithelial keratin and filaggrin expression in seborrheic keratosis: evaluation based on histopathological classification.
abstract: OBJECTIVE
  Seborrheic keratosis (SK) is classified into six types: hyperkeratotic; acanthotic; irritated; clonal; reticulated; and adenoid. However, the origins of the respective types of SK remain unclear.
  
  
  METHODS
  To clarify the histogenetic origins of SK, we performed immunohistochemical studies of keratin (K) and filaggrin expression, taking into account the histopathological classifications of SK.
  
  
  RESULTS
  Hyperkeratotic SK mainly expressed K1, K10, and filaggrin. Acanthotic SK mainly expressed K14 with some K15. Irritated SK mainly expressed K14 and K17 in squamous eddies. Clonal SK, reticulated SK, and adenoid SK mainly expressed K14. The results show that hyperkeratotic SK differentiated towards squamoid terminal keratinization, whereas acanthotic, irritated, clonal, reticulated, and adenoid SK mainly differentiated towards basaloid undifferentiated cells. In addition, acanthotic SK differentiated towards the hair bulge, and irritated SK differentiated towards the follicular infrainfundibulum.
  
  
  CONCLUSIONS
  Based on the patterns of keratin and filaggrin expression demonstrated by the histopathological types, SK demonstrated diverse differentiation towards epidermal keratinization, basaloid cells, the infrainfundibulum and hair follicle bulges, which suggests that SK is in an undifferentiated and hyperproliferative state with heterogeneous differentiation. The immunohistochemical method of investigating patterns of keratin expression is useful in the differential diagnosis of cutaneous epithelial tumors.
authors.affiliation: Department of Dermatology, Hyogo College of Medicine, Nishinomiya, Japan.
authors.forename: Nobuko
authors.initials: N
authors.lastname: Yoshimi
authors.forename: Yasutomo
authors.initials: Y
authors.lastname: Imai
authors.forename: Ayako
authors.initials: A
authors.lastname: Kakuno
authors.forename: Airo
authors.initials: A
authors.lastname: Tsubura
authors.forename: Kiyofumi
authors.initials: K
authors.lastname: Yamanishi
authors.forename: Ichiro
authors.initials: I
authors.lastname: Kurokawa
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000378:metabolism; D001707:Biopsy, Needle; D005260:Female; D000091344:Filaggrin Proteins; D006801:Humans; D007150:Immunohistochemistry; D007381:Intermediate Filament Proteins / Q000032:analysis / Q000378:metabolism*; D007633:Keratins / Q000032:analysis / Q000378:metabolism*; D017492:Keratosis, Seborrheic / Q000145:classification* / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D012494:Sampling Studies; D012680:Sensitivity and Specificity
chemical_list: D015415:Biomarkers; C000717249:FLG protein, human; D000091344:Filaggrin Proteins; D007381:Intermediate Filament Proteins; D007633:Keratins