Centrosome amplification is frequently found in both solid tumors and hematological malignancies. Experimentally, supernumerary centrosomes can be induced by overexpression of polo-like kinase 4 (PLK4), the principal regulator of centriole replication. The image depicts a large human osteosarcoma cell, which harbors numerous spindle poles as a consequence of exogenous PLK4 overexpression. In early prophase, chromatin condensation is accompanied by the separation of centrosomes and recruitment of the mitotic kinesin Eg5 (green) to spindle poles and proximal asters. For details, see article by Konotop and colleagues on page 6690.