Midgut Carcinoids and Solid Carcinomas of the Intestine: Differences in Endocrine Markers and p53 Mutations

Fifteen midgut carcinoid tumors and 5 solid carcinomas of the intestine with carcinoid-like morphological features were evaluated histochemically and immunohistochemically with respect to various endocrine markers and expression of mutant p53 protein. Direct sequencing of the p53 gene after PCR amplification was carried out on microdissected cells from all tumors. All investigated carcinoid tumors showed chromogranin and argentaffin reaction, but lacked nuclear immunostaining with p53 antibodies. In 14 immunohistochemically negative midgut carcinoid tumors, no mutations were identified. One carcinoid tumor devoid of p53 staining was, however, found to contain mutation in exon 6 of the p53 gene. In contrast, the solid carcinomas were essentially chromogranin negative but all displayed clearly positive p53 staining in a variable number of cell nuclei. Sequence analysis of exons 5-8 of the p53 gene in the 5 carcinomas showed mutations in exons 6 and 7 in 2 tumors and in exon 8 in 2 other tumors, while no mutation was detected in the fifth tumor. The carcinoid tumors and the solid carcinomas of the small intestine are thought to derive histogenetically from endocrine cells and enterocytes, respectively. The present results substantiate that divergent mechanisms operate in the development of the two tumor types.