CDK4 and anaplastic large cell lymphoma: In the context of NPM-ALK(+) ALCL, ERK1/2 are known to drive proliferation by promoting cyclin-dependent kinase 4 (CDK) activity and phosphorylation of the retinoblastoma protein, and maintaining viability by positively regulating the expression of anti-apoptotic factors (e.g., Bcl-xL).