Copyright© 2015 International Institute of Anticancer Research (Dr. John G. Delinassios), All rights reserved.
Telomere lengths in normal human cells are tightly regulated within a narrow range. Telomere length abnormalities are prevalent genetic alterations in malignant transformation. We studied telomere length abnormalities, telomerase RNA component (TERC) expression, alpha-thalassemia X-linked mental retardation (ATRX) expression, and death domain-associated protein (DAXX) expression in gastroenteropancreatic neuroendocrine tumors (GEP-NETs). We used tissue microarrays to perform telomere fluorescent in situ hybridization (FISH) and TERC in situ hybridization in 327 formalin-fixed paraffin-embedded tissues of GEP-NETs. Telomere length abnormalities were detected in 35% of 253 informative cases by using telomere FISH. Ten cases had altered lengthening of telomeres (ALT), an ALT-positive phenotype (4%), and 79 cases had telomere shortening (31%). The ALT-positive phenotype was significantly associated with tumors of pancreatic origin (7/10) and loss of ATRX or DAXX protein (8/10). Telomere shortening was significantly associated with low TERC expression. In the survival analysis, loss of ATRX or DAXX protein was associated with a decreased overall survival. Multivariate regression analysis showed that lymph node metastasis and high TERC expression were independent prognostic factors of reduced overall survival (OS) for patients with GEP-NETs. Our results showed that telomere lengthening (the ALT-positive phenotype) and telomere shortening accompanied by low TERC levels are two types of clinically significant telomere abnormalities in GEP-NETs.