PLK1 and neoplasm: The combination of oxaliplatin and volasertib led to a significantly greater anti‐tumor effect (Figure 3I), which showed remarkably decreased Ki‐67 and increased cleaved‐caspase 3 by immunohistochemistry (IHC) analysis (Figure 3J). Furthermore, in two CRC patient‐derived xenograft (PDX) models in which high levels of PLK1 and p‐PLK1 were detected by IHC analysis (Figure S3E, Supporting Information), drug combination treatment resulted in complete suppression of tumor growth compared to single treatment (Figure 3K,M) and the proliferation marker Ki‐67 was significantly decreased (Figure 3L,N).