Ablation of CDK6 and STAT5B rewires T cell developmental dynamics and prevents ALK+ lymphoma formation.

CDK6 and STAT5B are well-established oncogenic drivers, but their interplay during transformation remains poorly understood. Here, we demonstrate that simultaneous genetic deletion of Cdk6 and Stat5b in an NPM-ALKTg/+ mouse model completely prevents tumor formation. Immature DN2/3 thymocytes are identified as the cellular origin of ALK-driven malignancy. Single-cell transcriptomics reveals a tumor-specific differentiation trajectory that is fully disrupted by combined Cdk6/Stat5b loss, coinciding with a developmental shift. We uncover shared transcriptional targets of CDK6 and STAT5B involved in cell-cycle regulation and apoptosis at the tumor initiation stage. In human ALCL cells, dual deletion of CDK6 and STAT5B induces context-dependent synthetic lethality, exposing a potential therapeutic vulnerability. A transcriptional signature derived from CDK6/STAT5B-dependent tumor initiation genes identifies a high-risk subgroup of ALCL patients with worse survival. Together, these findings establish a molecular link between thymocyte development, the crosstalk of CDK6 and STAT5B, oncogenic signaling, and clinical outcome in ALCL.