The shift on energetic demands of proliferating cells during tumorigenesis requires an intense crosstalk between cell cycle and metabolism. Beyond their role in cell proliferation, cell cycle regulators also modulate intracellular metabolism of normal tissues. Using both genetic and pharmacological approaches, we aimed to determine the metabolic role of CDK4 in TNBC cells. Unexpectedly, deletion of CDK4 only slightly reduces cell proliferation of triple negative breast cancer (TNBC) cell line and allows in vivo tumor formation. Furthermore, pro-apoptotic stimuli fail to induce proper cell death in CDK4-silenced, depleted or long-term CDK4/6 inhibitors-treated TNBC cells, with dampened mitochondrial calcium uptake. In the first mass spectrometry-based experiment linked to this project, we explored the proteome and phosphoproteome of WT vs CDK4 KO in triple negative breast cancer cells (MDA-MB-231).