title: Comparison of CD23 staining patterns in Merkel cell carcinoma and non-cutaneous small cell carcinoma.
abstract: BACKGROUND
  During our daily practice, we observed that cluster designation 23 (CD23) (clone BU38) labels Merkel cells in normal skin. In this study, we examined the expression of CD23 in Merkel cell carcinoma (MCC) and assessed its usefulness in distinguishing MCC from non-cutaneous small cell carcinoma (SMCC).
  
  
  METHODS
  Immunohistochemical staining of CD23 was performed on a total of 33 MCCs, 22 SMCCs and 5 carcinoid tumors.
  
  
  RESULTS
  CD23 reactivity was present in 32 of 33 (97%) MCCs, 18 of 22 (82%) SMCCs and 5 of 5 (100%) carcinoid tumors. In MCC, 19 cases (59%) showed a predominance of perinuclear dot-like staining similar to cytokeratin 20, 3 (9%) showed mostly cytoplasmic staining and 10 (31%) displayed a combination of perinuclear dot-like and cytoplasmic staining. In contrast, all CD23-positive SMCCs and carcinoid tumors showed a diffuse cytoplasmic staining. There was a significant difference in the CD23 staining patterns between MCC and SMCC (p < 0.0001).
  
  
  CONCLUSIONS
  CD23 is expressed in the majority of MCC, SMCC and carcinoid tumor irrespective of clinical outcome. The distinct punctate CD23 staining for MCC may be helpful in differentiating it from SMCC. To our knowledge, this is the first study to show the expression of CD23 in neuroendocrine tumors.
authors.affiliation: Department of Pathology, University of Michigan Medical Center, Ann Arbor, MI 48109-0602, USA.
authors.forename: Jason
authors.initials: J
authors.lastname: Carvalho
authors.forename: Douglas
authors.initials: D
authors.lastname: Fullen
authors.forename: Lori
authors.initials: L
authors.lastname: Lowe
authors.forename: Lyndon
authors.initials: L
authors.lastname: Su
authors.forename: Linglei
authors.initials: L
authors.lastname: Ma
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002276:Carcinoid Tumor / Q000378:metabolism* / Q000473:pathology; D015266:Carcinoma, Merkel Cell / Q000378:metabolism* / Q000473:pathology; D018288:Carcinoma, Small Cell / Q000378:metabolism* / Q000473:pathology; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008297:Male; D008875:Middle Aged; D017455:Receptors, IgE / Q000096:biosynthesis*; D012878:Skin Neoplasms / Q000378:metabolism* / Q000473:pathology
chemical_list: D017455:Receptors, IgE