Investigating the Use of Circulating Tumor DNA for Sarcoma Management

Background/Objectives: Sarcomas are a heterogeneous group of cancers, many with high rates of recurrence and metastasis, leading to significant morbidity and mortality. Due to a lack of early diagnostic biomarkers, by the time recurrent disease can be clinically detected, it is often extensive and difficult to treat. Here, we sought to investigate methods of detecting ctDNA in sarcoma patient plasma to potentially monitor disease recurrence, progression, and response to treatment. Methods: Whole-exome sequencing of matched tumor and blood samples revealed patient-specific mutations, which were used to develop personalized assays to detect ctDNA in patient plasma. Since ctDNA is present in extremely low quantities, detection requires highly sensitive methodologies. Droplet digital PCR is highly sensitive; however, it is limited in that it can only be used to target one tumor variant at a time. Therefore, a protocol combining multiplex PCR and targeted amplicon sequencing was developed. Results: ddPCR was successfully able to detect tumor-specific mutations in plasma, confirming the presence of ctDNA in sarcoma patients. Multiplex PCR followed by amplicon sequencing was able to detect multiple tumor variants simultaneously, although it was not as sensitive as ddPCR. Additionally, ctDNA was detected in patient plasma collected at two different time points. Conclusions: This work demonstrates that although there is a lack of recurrent biomarkers, personalized assays detecting ctDNA have the potential to be used to monitor disease progression in sarcoma.