EWSR1 and osteosarcoma: Consistent with the gene expression data, all five EWS cell lines tested (TC106, TC32, A673, SK-ES-1, and RD-ES) expressed relatively high levels of MERTK protein compared to the weaker expression of MERTK in the osteosarcoma cell line U2OS, which was used as a positive control for TAM kinase expression (Figure 2C).