Anaplastic lymphoma kinase-positive anaplastic large cell lymphoma with the variant RNF213-, ATIC- and TPM3-ALK fusions is characterized by copy number gain of the rearranged ALK gene.

Anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma is characterized by 2p23/ aberrations, including the classic t(2;5)(p23;q35)/ rearrangement present in ~80% of cases and several variant t(2p23/ALK) occurring in the remaining cases. The fusion partners play a key role in the constitutive activation of the chimeric protein and its subcellular localization. Using various molecular technologies, we have characterized ALK fusions in eight recently diagnosed anaplastic large cell lymphoma cases with cytoplasmic-only ALK expression. The identified partner genes included (one case), (one case), (four cases) and (two cases). Notably, all cases showed copy number gain of the rearranged gene, which is never observed in -positive lymphomas. We hypothesized that this could be due to lower expression levels and/or lower oncogenic potential of the variant fusions. Indeed, all partner genes, except , showed lower expression in normal and malignant T cells, in comparison with In addition, we investigated the transformation potential of endogenous Npm1-Alk and Atic-Alk fusions generated by clustered regularly interspaced short palindromic repeats/Cas9 genome editing in Ba/F3 cells. We found that Npm1-Alk has a stronger transformation potential than Atic-Alk, and we observed a subclonal gain of after a longer culture period, which was not observed for Taken together, our data illustrate that lymphomas driven by the variant ATIC-ALK fusion (and likely by RNF213-ALK and TPM3-ALK), but not the classic NPM1-ALK, require an increased dosage of the hybrid gene to compensate for the relatively low and insufficient expression and signaling properties of the chimeric gene.