[688] 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:

Immunohistochemistry results for primary rectal NETs, n = 36
Staining intensityIslet 1 (%)PAX8 (%)CDX2 (%)Chromogranin A (%)Synaptophysin
Moderate to strong28 (78)24 (67)015 (42)35 (97)
All (weak, moderate, strong)30 (83)28 (78)015 (42)36 (100)

The majority of tumors were immunoreactive with Islet 1 and PAX8 and showed moderate to strong staining. There was no difference between the rates of expression of Islet 1 (83%) and PAX8 (78%) in primary rectal NETs (p=0.77). Although results of staining for Islet 1 and PAX8 were concordant in the majority of cases, discordant staining was observed in 4 tumors. None of the tumors were positive for CDX2. Almost all tumors positive for chromogranin A and synaptophysin showed moderate to strong staining intensity. A significantly greater number of rectal NETs showed expression of synaptophysin (100%) compared to chromogranin A (42%) (p<0.0001).
Conclusions: Islet 1 and PAX8 are both highly expressed in primary rectal NETs, at rates similar to what we have seen previously for primary pancreatic NETs (Islet 1, 82%; PAX8, 88%). Synaptophysin expression is seen significantly more commonly than chromogranin A in primary rectal NETs.
Category: Gastrointestinal

Tuesday, March 20, 2012 1:00 PM

Poster Session IV # 69, Tuesday Afternoon


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