LAUSR

CNS-associated tumors are notoriously difficult to detect in plasma. Chordomas are the most common primary spinal column malignancy, and extensive surgical procedures, along with chemotherapy and radiation are required to reduce recurrence. Currently CT, MRI, and PET are used to monitor for recurrence but are limited by surgical sequalae. In addition, needle biopsy risks tumor seeding along the biopsy track. In the largest cohort of chordomas described thus far, we characterize the mutational landscape of these tumors and show that liquid biopsy is a sensitive method for detecting cancers. 34 patients with a biopsy-confirmed diagnosis of chordoma had blood drawn before surgery, at the time of surgery, and/or at follow up appointments. Mutations in the primary tumor were identified by whole exome sequencing (WES) and droplet digital PCR (ddPCR) and/or Rapid Amplification of cDNA Ends Sequencing (RACE-Seq) was used to detect one or more of these mutations in plasma ctDNA at concurrent or later time points. The primary endpoint was detection of mutations in ctDNA in biopsy-confirmed chordoma samples. 87.9% of patients were ctDNA positive at the time of initial blood draw (p < 0.001). Follow up blood draws in twenty of the patients demonstrated that ctDNA levels reflected the clinical status of the disease. Patients with positive ctDNA levels were more likely to undergo radiotherapy (p = 0.004), and the presence of ctDNA may predict response to systemic chemotherapy and/or disease recurrence. Given the significant sequelae of biopsy and spinal surgery, liquid biopsy may be the best tool for detection and monitoring of chordomas.