ALK and anaplastic large cell lymphoma: The main feature of ALK+ ALCL is the expression of ALK fusion proteins such as nucleophosmin (NPM)–ALK, TNF receptor-associated factor (TRAF)1–ALK, 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/IMP cyclohydrolase ATIC–ALK, ring finger protein (RNF)213–ALK, and tropomyosin (TPM)3–ALK (3–6).