Gastric neuroendocrine neoplasms: tumour clonality and malignancy-associated large X-chromosomal deletions

Type I gastric carcinoid tumours associated with corporal (body of stomach) atrophic gastritis (CAG) are benign tumours developing as the final step of a hyperplastic precursor sequence. The neoplastic nature of these tumours has been assumed but never proved. Type III gastric carcinoid tumours and neuroendocrine carcinomas are malignant neoplasms without known precursor lesions. To assess the neoplastic nature of type I carcinoids, the clonal status of 35 tumours from 23 female patients was investigated using the human androgen receptor (HUMARA) gene test, which is based on the pattern of X-chromosome inactivation. For comparison, the same test was also performed on four type III carcinoids and two neuroendocrine carcinomas. DNA extracted from paraffin sections was digested with Hha I restriction enzyme and then amplified by polymerase chain reaction (PCR) using established HUMARA primers. The PCR products were analysed in an automated DNA sequencer. In a complementary analysis of the same tumours, loss of heterozygosity (LOH) on the X chromosome was studied using three polymorphic markers (DXS989, DXS1003, DXS1192) in a PCR-microsatellite-based technique. After exclusion of non-informative cases, 14 of 16 type I carcinoids were found to be monoclonal on the basis of the pattern of X-chromosome inactivation. Monoclonality was also documented in one of three type III carcinoids and in the single neuroendocrine carcinoma, on the basis of LOH at the HUMARA locus, which per se can be regarded as evidence for clonality. Extensive LOH of the X chromosome involving at least two markers, was found in all metastasizing tumours (two type III carcinoids and two neuroendocrine carcinomas), but in none of the 27 benign carcinoids of types I and III. These results indicate that most type I carcinoids are true monoclonal neoplasms and that malignant evolution in gastric neuroendocrine tumours is associated with extensive allelic deletion of one X chromosome.