(P 226) SIGNATERA TESTING TO IDENTIFY MINIMAL RESIDUAL DISEASE IN HIGH GRADE SARCOMA

Objective: Soft tissue sarcomas are a rare group of tumors accounting for more than 150 different subtypes. Slightly more than half of sarcomas are diagnosed at early stage with 5-year survival rate of 81%. Approximately 20% are found at the locally advanced stage (stage 3) with 5-year survival rates ranging from 25-58%. Tumors presenting large (>5 cm), intermediate to high grade, and more aggressive subtypes have high early relapse rates necessitating active surveillance. Current surveillance involves physical exam and radiologic imaging which can be inconclusive and necessitate additional imaging and radiation exposure. Non-invasive biomarkers are needed to better monitor disease recurrence and responses to treatment. Signatera is a highly sensitive custom-built circulating tumor DNA (ctDNA) test for treatment monitoring and molecular residual disease (MRD) assessment in patients previously diagnosed with cancer, designed for each patient to help identify relapse earlier than standard surveillance. Our institution utilized this technology on our sarcoma patients and here we report on how the clinical courses of our patients were altered based on Signatera test results.

Methods: We performed standard of care for 32 high-grade/high risk soft tissue sarcoma patients who were treated locally and monitored with close surveillance consisting of physical examination and frequent imaging. In between scans patients received Signatera ctDNA testing. Radiology interpretation was performed by radiologists who specialize in sarcoma. Additional methods will be presented at CTOS.

Results: Our cohort consisted of 21 male (65.6%) and 11 female (52.4%) patients. Of the 32 sarcoma patients being followed for MRD using Signatera testing, we had 86 surveillance tests, of which 49 had associated imaging. There was a match in Signatera result and subsequent image result in 46 out of 49 cases (94.0%). We identified 3 patients who had evidence of MRD prior to a scheduled scan. Updated results with more patients and outcomes will be reported at CTOS and will include imaging.

Conclusion: Utilizing ctDNA technologies such as Signatera can potentially significantly improve patient outcomes. In this pilot study, our findings were similar to previously reported data by the Standford group. With short interval follow up, there were 3 patients that had earlier detection of their recurrent sarcoma than seen on imaging which altered their disease course. In addition, our preliminary data showed that all of negative ctDNA correlated with imaging results. Updated results with more patients and outcomes will be reported in the updated abstract. Further studies are warranted especially to investigate if early detection and help treating physicians make decisions about the controversial use of adjuvant chemotherapy for high-risk soft tissue sarcomas.