Genetic studies of endocrine abdominal tumors

Sammanfattning: Pancreatic endocrine tumors (PETs) occur sporadically or in the familial multiple endocrine neoplasia type 1 (MEN1) syndrome, whereas midgut carcinoids are nonfamilial, malignant endocrine tumors of the intestine. For these tumor entities morphological criteria are of limited use for prognostic prediction and selection of treatment. Genetic characterization may give additional information of clinical use and reveal pathways involved in tumor development.Molecular genetic alterations in sporadic and MEN1-associated PETs and midgut carcinoids were studied with LOH and mutational analysis. In addition, immunohistochemistry was used to clarify gene expression. Detected genetic aberrations were correlated to the disease course of individual patients.Somatic mutations of the MEN1 gene at chromosome 11q13 were detected in 1/3 of sporadic PETs. Moreover, LOH was found in 70% of the lesions. All tumors with somatic MEN1 mutations displayed loss of the remaining allele showing that the MEN1 gene is involved in development of sporadic PETs. Sporadic and MEN1 PETs were analyzed for LOH at 3p, 11q13 and 18q. A relation of LOH at 11q13 and 3p to malignancy was found for the sporadic tumors. None of the benign tumors (all of them insulinomas) had allelic loss at 3p or 11q13, versus 92 % (p<0.01) of the malignant tumors (including malignant insulinomas). 1/4 of both sporadic and MEN1 lesions displayed LOH at 18q, without altered Smad4/DPC4.Genome-wide LOH screening of MEN1 PETs revealed multiple allelic deletions without general correlation to tumor size or malignancy. All tumors displayed LOH at the MEN1 locus, and 30% on chromosomes 3, 6, 8, 10, 18 and 21. Intratumoral heterogeneity was revealed, with chromosome 6 and 11 deletions in most tumor cells. Chromosome 6 deletions were mainly found in lesions from patients with malignant features. A similar genome-wide LOH screening was performed on midgut carcinoids. Deletions at chromosome 18q were found in 88% of the tumors indicating a potential tumor suppressor locus.