3.6 Circulating Tumor DNA
Figure 3 shows change in ctDNA levels over time for patients
with osteosarcoma (panel A ) and Ewing sarcoma (panelB ). All four patients with osteosarcoma and available baseline
samples had detectable ctDNA >10% (median 16.9%, range
12.4% – 35.5%). Levels decreased during therapy in two osteosarcoma
patients and increased during therapy in the other two patients. Of
these two patients, one had stable disease at re-evaluation and one was
not able to be re-evaluated. A fifth patient without a baseline sample
had detectable ctDNA at cycle 1 day 3 that subsequently decreased during
therapy. ctDNA was detectable in 5/7 patients with Ewing sarcoma, with a
median percent ctDNA level of 2.11 (range 0.31 – 54.08) among those 5
patients. Of the five patients with detectable ctDNA at baseline, levels
increased in one patient with clinical progression. In the other four
patients, levels either decreased and remained low throughout therapy or
were low at baseline and remained low throughout therapy. The sole
patient with Ewing sarcoma who had a partial response did not have
detectable ctDNA at baseline or during therapy.