Abstract
418 Background: Telomeres (T) consist of thousands of copies of TTAGGG tandem repeats capping the ends of the chromosome. T along with enzyme telomerase provides protection against any threats to the genome that might arise as a consequence of “end replication problem.” During aberrant cell proliferations the normal check points of cell cycle is compromised leading to unrestricted cell division with extremely short T and subsequent genomic instability. Studies have linked short TL with premalignant and malignant stages of CRC carcinogenesis. However, the relation of TL to the clinical outcomes has not been conclusively determined. In this study we evaluated the association of TL with clinical outcomes in a cohort of 75 CRC patients. Methods: Tumor DNA was isolated from formalin fixed paraffin embedded specimens. TL was measured by using a qRT-PCR method that provided the relative T copy number, compared to reference copy number of the housekeeping gene, β-Globin, which resulted in a T/S ratio. One T/S ratio unit is equivalent to a mean TL of 4,270 base pairs (BP). Results: From 75 patients, 122 tissue samples were identified (66 primary, 52 metastases, 29 matched pairs). Age at diagnosis (>/< median) had a statistically significant difference in TL (mean BP 4700 vs. 4374; p=0.05) with shorter TL in the advanced age. Females had longer TL compared to men (mean BP 4722 vs. 3669 respectively; p=0.04). Shorter TL was associated with shorter progression free survival (PFS) for patients treated with cetuximab/panitumumab (3963 vs. 5295 p=0.04). There was a trend towards increased overall survival (>/< median) with longer TL (4934 vs. 4117; p=0.08). We failed to find a difference in the TL between primary and metastatic sites in the 29 patients with paired samples. Conclusions: TL is a potential biomarker predictive of clinical outcome (PFS) for patients treated with cetuximab/panitumumab. Tumor TL reduces with advancing age and appears to be sex dependent. Further studies to validate TL’s predictive role in patient outcomes are underway.
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