Detection of Alternative Lengthening of Telomeres via Chromogenic in situ Hybridization (ALT-CISH) for the Prognostication of PanNETs and Other Neoplasms

Abstract

Molecular studies have shown ALT to be an important prognostic biomarker of shorter relapse-free survival (RFS) for patients with pancreatic neuroendocrine tumors (PanNETs) and other neoplasms. However, the preferred method of detecting ALT in tissue is by fluorescence in situ hybridization (FISH), which has several clinical limitations. These issues necessitate the creation of a chromogenic ALT assay that can be easily implemented into routine practice. A CISH assay was developed using genetically modified osteosarcoma cell lines, 20 normal pancreata, 20 ALT-positive PanNETs, and 20 ALT-negative PanNETs. Thereafter, it was validated on a multi-institutional cohort of 360 surgically resected PanNETs and correlated with multiple clinicopathologic features, RFS, and FISH results. Separately, 109 leiomyosarcomas (LMS) were evaluated by both CISH and FISH, and, similarly, the prognostic significance of ALT status was assessed. Upon optimization, ALT-CISH was identified in 112 of 360 (31%) primary PanNETs and was 100% concordant with FISH testing. ALT correlated with several adverse prognostic findings and distant metastasis (all p<0.004). The 5-year RFS for patients with ALT-positive PanNETs was 35% as compared to 94% for ALT-negative PanNETs. By multivariate analysis, ALT was an independent prognostic factor for shorter RFS. Similarly, ALT was associated with shorter RFS in LMS patients and, analogous to PanNETs, a negative, independent prognostic factor. ALT-CISH was developed and validated in not only PanNETs, but also sarcomas, specifically LMS. CISH testing has multiple advantages over FISH that facilitate its widespread clinical use in the detection of ALT and prognostication of patients with diverse neoplasms.