Prevalence of Alternative Lengthening of Telomeres (ALT) in Pediatric
Sarcomas Determined by the Telomeric DNA C-circle Assay
Abstract
Background: Alternative lengthening of telomeres (ALT) occurs
in sarcomas and ALT cancers share common mechanisms of therapy
resistance or sensitivity. Telomeric DNA C-circles are self-primed
circular telomeric repeats detected with a PCR assay that provide a
sensitive and specific biomarker exclusive to ALT cancers. We have
previously shown that 23% of high-risk neuroblastomas are of the ALT
phenotype. Here, we investigate the frequency of ALT in Ewing’s family
sarcoma (EFS), rhabdomyosarcoma (RMS), and osteosarcoma (OS) by
analyzing DNA from fresh frozen primary tumor samples utilizing the
real-time PCR C-circle Assay (CCA). Methods: We reviewed prior
publications on ALT in pediatric sarcomas. DNA was extracted from fresh
frozen primary tumors, fluorometrically quantified, C-circles were
selectively enriched by isothermal rolling cycle amplification and
detected by real-time PCR. Results: The sample cohort consisted
of DNA from 95 EFS, 191 RMS, and 87 OS primary tumors. One EFS and 4 RMS
samples were inevaluable. Using C-circle positive (CC+) cutoffs
previously defined for high-risk neuroblastoma, we observed 0 of 94 EFS,
5 of 187 RMS, and 62 of 87 OS CC+ tumors. Conclusions:
Utilizing the ALT-specific CCA we observed ALT in 0% of EFS, 2.7% of
RMS, and 71% of OS. These data are comparable to prior studies in EFS
and OS using less specific ALT markers. The CCA can provide a robust and
sensitive means of identifying ALT in sarcomas and has potential as a
companion diagnostic for ALT targeted therapeutics.