Upon nuclear entry together with STAT5B, PAK1 co-transactivated the pro-angiogenic CSF2 gene, encoding granulocyte-macrophage colony stimulating factor 2 (a.k.a GM-CSF), to increase CSF2 expression, hence enhancing angiogenesis in myxofibrosarcomas. Here, STAT5B is linked to myxofibrosarcoma.