Immunohistochemical Staining of Rectal Neuroendocrine Tumors Overlaps with Pancreatic Neuroendocrine Tumors
Jamie Koo, Elizabeth Moschiano, Richard Mertens, Deepti Dhall. Cedars-Sinai Medical Center, Los Angeles, CA
Background: Neuroendocrine tumors (NETs) can present as liver metastases before discovery of the primary tumor. In our recent study with Islet 1 and PAX8, two markers of NETs of pancreatic origin, we observed aberrant immunoreactivity in primary rectal NETs with both Islet 1 and PAX8. Previous studies in the literature have reported that chromogranin A is infrequently expressed in rectal NETs. The purpose of this study was to further characterize the immunohistochemical staining patterns of primary rectal NETs with Islet 1, PAX8, CDX2, chromogranin A, and synaptophysin.
Design: A total of 36 primary rectal well-differentiated NETs from 32 patients were studied. Immunohistochemistry was performed with antibodies against Islet 1, PAX8, CDX2, chromogranin A, and synaptophysin. The extent of positive staining was assessed, and the intensity of staining was evaluated as weak, moderate, or strong. Tumors showing moderate to strong staining of at least 5% of cells or showing weak staining of at least 10% of cells were considered positive.
Results: Immunohistochemistry results separated according to staining intensity are summarized below:
|Staining intensity||Islet 1 (%)||PAX8 (%)||CDX2 (%)||Chromogranin A (%)||Synaptophysin|
|Moderate to strong||28 (78)||24 (67)||0||15 (42)||35 (97)|
|All (weak, moderate, strong)||30 (83)||28 (78)||0||15 (42)||36 (100)|