To further define the subset of tumours susceptible to respond to PLK1 inhibition, we tested the anti-tumour activity of volasertib as compared to palbociclib in three additional PDX with amplification or CN gain of CCND1. PDX HBCx-124 was established from a young patient diagnosed with metastatic BC at 26 years old. This evidence concerns the gene CCND1 and breast cancer.