Value of ctDNA in the Treatment of Multiple Primary Cancers

This trial is a single-center, prospective, exploratory study.The objective is to study the peripheral blood circulating tumor DNA (CT-DNA) gene profile of patients with multiple primary tumors (MPC) and to evaluate the exploratory study for guiding drug selection. Patients with multiple primary tumors who met the inclusion criteria and did not meet the exclusion criteria will be enrolled in this study. CtDNA test will be used for CT-DNA gene profile study, and whether the test results can guide drug selection will be evaluated.The expected enrollment time is 12 months, and clinical observation is performed until disease progression and patient death.Additional CT-DNA tests will be performed as the disease progresses (2 cT-DNA tests in total).