RET and fibrosarcoma: SC is considered an NTRK fusion-positive cancer, together with SC of the breast and infantile fibrosarcoma.[47] When the normal NTRK gene is fused with another gene to form an NTRK fusion gene, the tropomyosin receptor kinase (TRK) fusion protein is produced, which continuously activates the phosphoinositide phospholipase Cɣ, Mitogen-activated protein kinase, and Pl3K signal transmission pathways and promotes cancer cell proliferation.[47,48] More recently, Skalova et al reported VIM-RET gene fusion in SC,[49] and this finding may further expand the molecular definition of SC.