RB1 and cervical cancer: But, it could be proven that also the E6 oncogene of high and low risk HPV types is able to generate elevated Cyclin A1 expression through phosphorylation of pRb. Santopietro et al. could identify protein expression of Cyclin A as independent predictor of high-risk HPV and high-risk HPV associated high-grade lesions in cervical cancer [18].