CDK4 and neoplasm: Key kinases regulating cell cycle G1 progression were also altered in different CTC samples including cyclin-dependent kinase 6 (CDK6, chr7) gain in CTC 1 of P43 and in single CTCs of P50, and cyclin-dependent kinase 4 (CDK4, chr12) gains in 5/7 CTCs of P45 and the corresponding tumor biopsy.