Background and aims: 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 histopathologic and immunohistochemical characteristics of two cases of composite ITAC with small cell carcinoma.
Methods: Two cases of composite ITACs 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 tumor 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 were positive for CAM5.2, AE1:AE3, CK7, CK20, and CK19 whereas only the small cell carcinoma expressed synaptophysin and CD56. Both components were negative for CDX-2, villin, CD99, and p63. The “signet-ring” cells were positive for chromogranin and synaptophysin. The second tumor showed a papillary-type ITAC combined with a small cell carcinoma. The adenocarcinoma and the small cell carcinoma were positive for CAM5.2, AE1:AE3, CK7, CK19, and CK20. Only the adenocarcinoma was CDX-2 positive whereas the small cell carcinoma expressed CD56, and synaptophysin.
Conclusion: Both components of combined ITACs and neuroendocrine small cell carcinoma show significant immunohistochemical overlap to support a common origin. The occurrence of a distinct neuroendocrine carcinoma combined with ITACs expands the histopathologic spectrum of these tumors.