2A), with additional types (68, 73)[41], [42] and [43] being recognised as ‘possibly’ cancer-causing (category 2 in Fig. 2A). Several other HPV types also belong to the high-risk clade based on evolutionary similarity to the known cancer-causing types [44] and [45] (shaded pink in Fig. 2A), although RO4929097 chemical structure so far, the epidemiological data confirming this have not been obtained. Recent studies also suggest that variant lineages may differ in risk of persistence and association with high-grade disease. Together, these viruses cause approximately half a million cases of

cervical cancer per year worldwide, with approximately half of these being fatal (530,000 cases per year with 275,000 deaths [WHO/ICO Information Centre on Human Papilloma Virus (HPV) and Cervical Cancer; http://www.who.int/hpvcentre/en/]). Importantly, these viruses are also associated with cancers at other sites, including the penis in men, the vagina and vulva in women and, in both genders, the anal transformation zone, the tonsils, oropharynx and base of tongue. It appears that deregulation of Rucaparib in vitro viral gene expression may occur to different extents at the different sites of high-risk HPV infection, and that squamo-columnar junctions, such as the cervical transformation zone, are

particularly prone to neoplastic disease. Nevertheless, high-risk HPVs do not cause cancer in the vast majority of the individuals that they infect [3] and [24]. As with all HPV infections, the high-risk types are maintained in the general population because of productive infections rather than inadvertent cancers. Low-grade squamous intraepithelial lesions (LSIL), where infectious particles are produced, are generally flat and inconspicuous, Megestrol Acetate and in most cases these will regress spontaneously within 18 months [4], [46] and [47]. For reasons that we do not yet clearly understand,

the high-risk HPV types have evolved the ability to persist, often for many years, and to drive cell proliferation in the basal and parabasal cell layers at some sites of infection [48] and [49]. This is not a prerequisite for virus production, and does not happen to any extent in lesions caused by low-risk types. High-grade lesions (high-grade squamous intraepithelial lesions; HSIL) are abortive infections in which normal patterns of early virus gene expression are perturbed [29]. In particular, it is thought that an elevation in the level of E6 and E7 is directly related to the increasing severity of neoplasia [50], and that the deregulated expression of these genes is directly responsible for the accumulation of genetic errors in the infected cell and the eventual integration of viral episomes into the host cell chromosome [51], [52] and [53], which is seen in many cervical cancers [53], [54], [55], [56] and [57].