ALK and neoplasm: For example, in anaplastic large cell lymphoma (ALCL), TCR rearrangement analyses identified malignant transformation of tumor cells in thymocytes prior to TCR β-rearrangement, but RAG-independent TCR expression driven by the oncogenic NPM-ALK fusion protein still allowed these cells to exit the thymus, and downregulation of the TCR was required for subsequent lymphomagenesis [73].