Different gene expression profiles in metastasizing midgut carcinoid tumors

• The genetic events leading the progression of midgut carcinoid tumors are largely unknown. The disease course varies from patient to patient, and there is a lack of reliable prognostic markers. In order to identify genes involved in tumor progression, gene expression profiling was performed on tumor specimens. Samples comprised 18 primary tumors, 17 lymph node (LN) metastases, and seven liver metastases from a total of 19 patients. Patients were grouped according to clinical data and histopathology into indolent or progressive course. RNA was subjected to a spotted oligo microarray and B-statistics were performed. Differentially expressed genes were verified using quantitative real-time PCR. Self-organizing maps demonstrated three clusters: 11 primary tumors separated in one cluster, five LN metastases in another cluster, whereas all seven liver metastases, seven primary, and 12 LN metastases formed a third cluster. There was no correlation between indolent and progressive behavior. The primary tumors with Ki67>5%, with low frequency of the carcinoid syndrome, and a tendency toward shorter survival grouped together. Primary tumors differed in expression profile from their associated LN metastases; thus, there is evidence for genetic changes from primary tumors to metastases. ACTG2, GREM2, REG3A, TUSC2, RUNX1, TPH1, TGFBR2, and CDH6 were differentially expressed between clusters and subgroups of tumors. The expression profile that assembles tumors as being genetically similar on the RNA expression level may not be concordant with the clinical disease course. This study reveals differences in gene expression profiles and novel genes that may be of importance in midgut carcinoid tumor progression.

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