Poster Presentation Advances in Neuroblastoma Research Congress 2016

Serum C-circles as biomarker of Alternative Lengthening of Telomeres (ALT) in neuroblastoma (#176)

Rebecca A Dagg 1 2 , Diana Ky 2 , Jeremy Henson 3 , Roger Reddel 1 4 , Loretta MS Lau 1 2 5
  1. University of Sydney, Sydney, Australia
  2. Children's Hospital at Westmead, Westmead, NSW, Australia
  3. University of New South Wales, Randwick, Australia
  4. Children's Medical Research Institute, Westmead, NSW, Australia
  5. Sydney Children's Hospital, Randwick, NSW, Australia

Unlimited proliferation of cancer cells requires activation of one of two telomere maintenance mechanisms: telomerase or homologous recombination-based ALT. C-circles (CC) (extrachromosomal partially single-stranded circular telomeric DNA) are a marker of ALT activity. We ask whether CC can be detected as cell-free circulating tumor DNA in the serum of patients with CC+ neuroblastoma tumor and can therefore be used as a serum ALT biomarker.

We first examined 149 high-risk neuroblastoma tumors and found 24% (n=36) of tumor DNA to be CC+, i.e. ALT+. The outcome of ALT+ neuroblastoma (all MYCN non-amplified) was as poor as that of MYCN-amplified neuroblastoma (n=55) (5-yr OS: 32% vs. 28%). Serum was available for analysis in a subset of 35 tumors where 40% (n=14) were CC+. CC were measured in the circulating DNA extracted from the serum (referred to as serum CC level). The amount of circulating DNA ranged from 8.6 to 373 ng/100uL of serum (median 46.2) and there was no significant difference in circulating DNA level between patients with CC+ and CC- tumor (median 41.5 vs. 47.4 ng/100uL; P=0.7).

Serum CC levels ranged from 1.2 to 1556 AU (median 50 AU) and there was no correlation between serum CC and circulating DNA levels (P=0.5). However, there was significant correlation between serum and tumor CC levels (P=0.001) and serum CC level was significantly higher in the CC+ than the CC- tumor group (median 340 vs. 25 AU; P<0.001). Serum CC for the normal control (individual with no known cancer) was 0.8 AU. In the ALT+ tumor group, 12 of 14 had serum CC >100 AU. In the ALT- tumor group, 3 of 21 has serum CC >100 AU. Using a cut-off of 100 AU, the sensitivity of serum CC for detecting ALT+ tumor was 86% (12/14), with specificity of 86% (18/21) and concordance 86% (30/35). The results of this study therefore support CC as a potential serum biomarker for ALT tumor activity.