Novel RET fusion molecules and uses are disclosed. In one embodiment, a KIF5B-RET fusion includes an in-frame fusion of an exon of KIF5B (e.g., one or more exons encoding a kinesin motor domain or a fragment thereof) and an exon of RET (e.g., one or more exons encoding a RET tyrosine kinase domain or a fragment thereof). For example, the KIF5B-RET fusion can include an in-frame fusion of at least exon 15 of KIF5B or a fragment thereof (e.g., exons 1-15 of KIF5B or a fragment thereof) with at least exon 12 of RET or a fragment thereof (e.g., exons 12-20 of RET or a fragment thereof).