Igor Latic

Date of Award

11-10-2006

Document Type

Open Access Thesis

Degree Name

Medical Doctor (MD)

First Advisor

Irvin M Modlin

Abstract

Objective: To utilize differential gene expression of candidate markers to discriminate benign APCs (APCs) from malignant and mixed cell APCs. Background Data: Considerable controversy exists in regard to the appropriate surgical management of APCs since standard clinical and immunohistochemical methods cannot reliably determine whether an APC is indolent or aggressive. We have identified five differentially expressed genes: nucleosome assembly protein 1-like 1 [NAP1L1]; melanoma antigen D2 [MAGE-D2]; metastasis-associated protein 1 [MTA1]; NAcht Leucine-rich-repeat Protein 1 [NALP1] and Chromogranin A [CgA] that define gut neuroendocrine (NE) Enterochromaffin (EC) cell behavior. We hypothesized that APC (APC) malignancy, also derived from EC cells, could be defined by using quantitative reverse transcriptase-polymerase chain reaction (QRT-PCR) and immunohistochemical approaches that evaluate potential marker genes. Methods: Total RNA was isolated using TRIzol reagent from 42 appendiceal samples including APCs identified at exploration for appendicitis (no evidence of metastasis; n=16), appendicitis specimens (n=11), malignant appendiceal tumors (>1.5cm, evidence of metastatic invasion; n=7) and mixed (goblet) cell appendiceal (GBC) adenocarcinoids (n=3), normal appendiceal tissue (n=5), and five colorectal cancers. Gene expression (CgA, NAP1L1, MAGE-D2, MTA1 and NALP1) was examined by Q-RT PCR (Applied Biosystems) and quantified against GAPDH. Results: CgA message was elevated (>1000-fold, p<0.05) in all tumor types. NAP1L1 was elevated (>10-fold, p<0.03) in both malignant and GBC adenocarcinoids compared to normal and incidental lesions (p<0.006). MAGE-D2 and MTA1 message were significantly elevated (>10-fold, p<0.01) in the malignant and GBC adenocarcinoid tumors but not in the appendicitis-associated carcinoids or normal mucosa. The apoptotic marker, NALP1, was over-expressed (>50-fold, p<0.05) in the appendicitis-associated and malignant APCs, but was significantly decreased (>10-fold, p<0.05) in GBC adenocarcinoids. Elevated CgA levels indicative of a carcinoid tumor were identified in one acute appendicitis sample with no histological evidence of a tumor. Conclusions: These data demonstrate that malignant APCs and GBC adenocarcinoids have elevated expression of NAP1L1 (mitotic regulation), MAGE-D2 (adhesion), and MTA1 (estrogen antagonism) compared to APCs identified at appendicitis. This, and the differences in NALP1 (apoptosis) gene expression (decreased in GBC adenocarcinoids), provides a series of molecular signatures that differentiate carcinoids of the appendix. CgA identified all appendiceal tumors as well as covert lesions, which may be more prevalent than previously recognized. The molecular delineation of malignant appendiceal tumor potential provides a scientific basis to define the appropriate surgical management as opposed to morphological assessment alone.

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This is an Open Access Thesis.

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