[587] Pseudoadenomatous Transformation of Tubal Gut Mucosa Secondary to Metastasis, Including a Unique Cytokeratin 7 Positive Type Not Previously Described

Cheryl Adackapara, Robert Odze. Brigham and Women's Hospital, Boston, MA

Background: Metastasis to the tubal gut may involve the mucosa in a manner that simulates adenomatous (in-situ) change, termed “pseudoadenomatous transformation” (PAT). As a result, metastatic tumors may be erroneously interpreted as primary lesions. We have noted, anecdotally, a previously undescribed type of PAT composed of non-neoplastic (reactive) epithelium that can also simulate in-situ change. The aim of this study was to evaluate the clinical, pathologic, and immunohistochemical features of patients with PAT of the tubal gut with particular emphasis on the type composed of reactive (non-neoplastic) epithelium.
Design: 54 tubal gut resection specimens identified via a 20 year search through the pathology files of a major university hospital coded as tubal gut metastasis (N>1000) were evaluated for the clinical, pathologic, and immunohistochemical features of the primary tumor and metastasis, and for evidence of PAT in the latter. Immunohistochemistry of the primary and secondary tumors was performed and included both general and tumor specific markers.
Results: Overall, 23 of 54 (43%) patients (M/F ratio: 1.1:1, mean age: 61 years) with tubal gut metastasis to the mucosa showed PAT. Metastatic tumors included adenocarcinomas from the small or large bowel (7/23), lung (3/23), pancreas/gallbladder (3/23), appendix (2/23), kidney (1/23), breast (1/23), uterus (1/23) and melanoma (5/23). PAT involved the small bowel more often than the large bowel (70% verus 30%; p=0.048). Microscopically, two patterns of PAT were detected; one in which metastatic neoplastic cells formed tubules or villi lined by basement membrane simulating in-situ disease [(9/23, 39%) (type A)], and the other in which peritumoral non-neoplastic epithelium revealed reactive (non-neoplastic) cytologic and architectural features simulating adenomatous epithelium [(11/23, 48% (type B)]. Three cases (13%) showed a mixture of both types of PAT. Peritumoral reactive PAT (type B) showed a previously unreported pattern of CK7 staining in 6/14, (43%) of cases, despite negativity in the normal epithelium, all type A PAT foci, and in the tumor metastasis (p<0.05).
Conclusions: Mucosal metastasis to the tubal gut may induce PAT either by direct cancerization of the mucosa, or by inducing a unique adenoma-like reactive atypia in the peritumoral epithelium which also showed upregulation (overexpression) of CK7. CK7 is helpful in identifying the latter and differentiating it from true neoplastic epithelium.
Category: Gastrointestinal

Monday, March 4, 2013 11:15 AM

Proffered Papers: Section D, Monday Morning


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