Conversely, the expression of fusion-related proteins was mostly unaffected after treatment (Figs 4A–C and S5), with one exception: mitofusin-1 (MFN1) was down-regulated in response to topotecan in NSTS-11 rhabdomyosarcoma cells and both osteosarcoma cell lines. The gene discussed is MFN1; the disease is osteosarcoma.