Zhang C, et al. - Researchers focused on the differential potential of polycyclic aromatic hydrocarbons (PAHs) as a co-factor in human papillomavirus (HPV)-mediated carcinogenesis, as well as on the possible mechanisms involved. They assessed the impact of 17 PAHs on high-risk HPV (HPV16). Primary cells extracted from baby rat kidney and treated with PAHs were used, on which HPV16 E7 oncogene was expressed. They assessed the impacts of PAHs on proliferation of HPV-null (C33A) and –infected (CaSki) as well as effects of PAHs on cell motility and invasivion of HPV-null (MCF7, C33A) and –infected (SiHa) cells. In the baby rat kidney cell system, the greatest co-transforming potential was demonstrated by benzo[a]pyrene (BaP), dibenz[a,h]anthracene (DBA) and indeno[1,2,3-cd]pyrene (IDP). There was no impact of short-term exposure to BaP, DBA, IDP and pyrene (PR) on proliferation of C33A or CaSki cells, however, long-term exposure resulted in dramatic increase in growth rate of CaSki cells by 120–140%. Overall, exposure to PAHs could be a key co-factor in HPV-related cancer development. On all three stages, namely initiation, promotion and progression, their action could be seen.