Since p21 and p27 have been reported to prevent the cyclin B-cdk1-driven progression of prostate cancer cells into G2/M [21], it is possible that long-term application of temsirolimus creates a negative feedback loop, causing suppression of p21 and p27, enhanced expression of cyclin B and cdk1, and accelerated mitotic progression. This evidence concerns the gene CDK1 and prostate cancer.