The purpose of SIBYL is to generate clinical validity data for the ability of a future version of Guardant360 developed by Guardant Health to measure response to systemic therapy in patients with unresectable advanced solid tumors. It is necessary to collect clinical data points and treatment outcomes in order to demonstrate clinical validity for longitudinal monitoring with ctDNA and correlation of ctDNA dynamics with therapeutic response, as evaluated by standard methods, including RECIST 1.1 and CT scan measurements.