e23170 Background: Centrosome amplification (CA) which refers to presence of supernumerary or abnormally large centrosomes is believed to drive tumor progression by promoting chromosomal instability and the generation of aggressive tumor clones that are more capable of rapid metastasis. Not much is known about factors that drive CA within solid tumors. We have previously shown the existence of rampant CA in triple-negative breast cancers (TNBCs).We report here thatintratumoral hypoxia, which is one of the major contributors to tumor heterogeneity, induces CA in TNBCs via HIF-1α. Methods: We immunohistochemically labeled 24 TNBC and adjacent normal tissue samples for HIF-1α and derived weighted indices (WIs) for nuclear HIF-1α. Adjacent serial sections from the same tumors were immunofluorescently labeled for the centrosomal marker γ-tubulin and CA was determined. Using public microarray datasets (Kao dataset, n = 327), we investigated whether centrosomal gene expression is enriched in breast tumors characterized by a hypoxia gene expression signature. Finally, to test the role of hypoxia in CA induction we exposed cultured TNBC cells (MDA-MB-231 and MDA-MB-468) to hypoxia and overexpressed (OE) or knocked out (KO) HIF-1α and quantitated CA. Results: A strong positive correlation was found between nuclear HIF-1α WI and CA in TNBC samples (Spearman’s rho p = 0.722, p < 0.001), and higher nuclear HIF-1α was associated with worse overall survival (p = 0.041; HR = 1.03). Furthermore, breast tumors with high expression of hypoxia-associated genes exhibited higher expression of centrosomal genes than breast tumors with low expression of hypoxia-associated genes. TNBC cells cultured in hypoxic conditions exhibited ~1.5 fold higher (p < 0.05) CA compared to cells cultured in normoxic conditions. Interestingly, level of CA decreased when HIF-1α KO TNBC cells were exposed to hypoxia; conversely, CA increased when HIF-1α OE TNBC cells were cultured in normoxic conditions. Conclusions: Thus,intratumoral hypoxia drives CA in TNBC via HIF-1α and contributes to poor outcomes. Determination of CA may help identify TNBC patients who could benefit from centrosome declustering drugs and HIF-1α inhibitors.