Genetic and clonal dissection of osteosarcoma progression and lung metastasis

Osteosarcoma is a primary malignant bone tumor that has a high potential to metastasize to lungs. Little is known about the mechanisms underlying the dissemination of OS cancer cells to lungs. We performed whole exome sequencing of 13 OS primary tumors, with matched lung metastases and normal tissues. Phylogenetic analyses revealed that lung metastatic tumors often harbor clones that are nonexistent or rare in the matched primary OS tumors. Spatially and temporally separated lung metastases were from parallel seeding events with a polyphyletic pattern. Loss of TP53 or RB1 is among the early events during OS tumorigenesis, while loss of PTEN is involved at the later stages associated with lung metastases. Finally, KEAP1 was identified as a novel biomarker for increased metastatic risk. Patients whose primary tumors harbored KEAP1 amplification have significantly poorer lung-metastasis free survival. This finding was validated in two independent datasets. Further, in vitro experiments exhibited that KEAP1 depletion suppressed the invasion of OS cells. Our findings uncover the patterns of clonal evolution during OS progression and highlight KEAP1 as a novel candidate associated with the risk of lung metastasis in OS patients.