Monitoring Response Using Circulating Tumor DNA in Undifferentiated Pleomorphic Sarcoma: A Case Report.

Circulating tumor DNA (ctDNA) can be used to assess treatment response in patients with undifferentiated pleomorphic sarcoma (UPS). The importance of this is explored in our case of a 75-year-old man who was diagnosed with UPS of the right kidney. After a right nephrectomy and tumor resection, the patient was recovering well with initially undetectable, and then slightly elevated, circulating tumor DNA. Abdominal pain started shortly before a scheduled magnetic resonance imaging (MRI) which revealed a large mass in the resection bed invading the liver. The patient was treated with gemcitabine and docetaxel chemotherapy, and the ctDNA level rose dramatically before gradually decreasing and eventually becoming undetectable. At surgery, pathologic examination of the re-resection specimen revealed a complete pathological response. ctDNA monitoring may be a useful tool for early detection of response to chemotherapy in patients with UPS.