Chaperonin-containing TCP-1 (CCT or TRiC) is a multi-subunit complex that folds many of the proteins essential for cancer development. CCT is expressed in diverse cancers and could be an ideal therapeutic target if not for the fact that the complex is encoded by eight distinct genes, complicating the development of inhibitors. Few definitive studies addressed the role of specific subunits in promoting the chaperonin's function in cancer. To this end, we investigated the activity of CCT2 (CCTβ) by overexpressing or depleting the subunit in breast epithelial and breast cancer cells. We found that increasing total CCT2 in cells by 1.3-1.8-fold using a lentiviral system, also caused CCT3, CCT4, and CCT5 levels to increase. Likewise, silencing cct2 gene expression by ~50% caused other CCT subunits to decrease. Cells expressing CCT2 were more invasive and had a higher proliferative index. CCT2 depletion in a syngeneic murine model of triple negative breast cancer (TNBC) prevented tumor growth. These results indicate that the CCT2 subunit is integral to the activity of the chaperonin and is needed for tumorigenesis. Hence CCT2 could be a viable target for therapeutic development in breast and other cancers. The hallmarks of cancer (uncontrolled proliferation, genomic instability, metastasis, etc.) reveal the complex nature of this disease and the challenges faced developing effective therapeutics 1,2. Cancer does, however, have an "Achilles heel" and that is its dependency or addiction on major cellular events or processes like transcription, translation, splicing, protein degradation and protein-folding 3. In healthy cells, such conserved and essential processes are rigorously regulated by the proteostasis network (PN) to ensure proteome balance. In order to maintain proteome integrity, the cellular proteome must be synthesized, folded into its native structure, and, when no longer needed, degraded and the amino acids recycled 4,5. Chaperones and chaperonins are key players in the PN 6. Unlike healthy, non-transformed cells, the PN of cancer cells is taxed to produce proteins involved in survival, angiogenesis, migration, proliferation which are essential for tumor formation, progression and metastasis. Cancer cells have a higher dependency on molecular chaperones and are uniquely challenged due to imbalances caused by chromosomal abnormalities and overexpression of oncogenes, ultimately leading to cellular stress 7. As example, inhibitors of Heat Shock Protein 90 (HSP90) showed promising outcomes in the treatment of metastatic breast cancer 8. However, despite being in clinical trials since 1998, the success of HSP90 inhibitors in clinical trials remains mixed 9-11. Reasons such as dose-limiting toxicity, incomplete inhibition of HSP90, and insufficient downregulation of client proteins impeded the clinical use of current HSP90 inhibitors 12,13. In recent years,