These agents inactivate CDKs 1, 2 and 9, as does SCH; roscovitine also inactivates CDK7, and flavopiridol is a pan-CDK inhibitor (CDKs 1, 2, 4, 6, 7 and 9).22, 23, 24, 25 Hsp90 inhibitors did not induce apoptosis when combined with PD0332991, which selectively targets CDK4 and CDK6 (Supplementary Figure 2c).26 This finding may be explained by redundant actions of PD0332991 and Hsp90 inhibitors: PD0332991 inactivates CDK4 and CDK6, and Hsp90 inhibitors downregulate CDK4 and CDK6.27, 28. Here, CDK6 is linked to spindle cell hemangioma.