title: Composite intestinal-type adenocarcinoma and small cell carcinoma of sinonasal tract.
abstract: OBJECTIVE
  Sinonasal intestinal-type adenocarcinomas (ITACs) are rare neoplasms resembling intestinal adenocarcinomas. Although several studies have documented neuroendocrine differentiation in ITACs, the combination of ITAC and small cell carcinoma has not been previously described in detail. The aim of this report is to detail the histopathological and immunohistochemical characteristics of two cases of composite ITAC with small cell carcinoma.
  
  
  METHODS
  Two cases of composite ITAC with small cell carcinoma were routinely processed, and representative sections were stained with CAM5.2, AE1:AE3, keratin 7, keratin 20, keratin 19, CDX-2, p63, villin, chromogranin, synaptophysin and CD56.
  
  
  RESULTS
  One tumour consisted of a mixed-type ITAC showing colonic-type and poorly differentiated adenocarcinoma with foci of "signet-ring" cells combined with small cell carcinoma. Both components stained positively with CAM5.2, AE1:AE3, CK7, CK20 and CK19, whereas only the small cell carcinoma expressed synaptophysin and CD56. Both components stained negatively with CDX-2, villin, CD99 and p63. The "signet-ring" cells stained positively with chromogranin and synaptophysin. The second tumour showed a papillary-type ITAC combined with a small cell carcinoma. The adenocarcinoma and small cell carcinoma stained positively with CAM5.2, AE1:AE3, CK7, CK19 and CK20. Only the adenocarcinoma was CDX-2 positive, whereas the small cell carcinoma expressed CD56 and synaptophysin.
  
  
  CONCLUSIONS
  The two components of the combined ITACs and neuroendocrine small cell carcinoma show significant immunohistochemical overlap, supporting a common origin. The occurrence of a distinct neuroendocrine carcinoma combined with ITACs expands the histopathological spectrum of these tumours.
authors.affiliation: Department of Pathology, University Health Network, University of Toronto, Ontario, Canada.
authors.forename: R
authors.initials: R
authors.lastname: Jain
authors.forename: V
authors.initials: V
authors.lastname: Gramigna
authors.forename: R
authors.initials: R
authors.lastname: Sanchez-Marull
authors.forename: B
authors.initials: B
authors.lastname: Perez-Ordoñez