Are 20 human papillomavirus types causing cervical cancer?

Abstract

In 2012, the International Agency for Research on Cancer concluded that there was consistent and sufficient epidemiological, experimental and mechanistic evidence of carcinogenicity to humans for 12 HPV types (HPV16, HPV18, HPV31, HPV33, HPV35, HPV39, HPV45, HPV51, HPV52, HPV56, HPV58 and HPV59) for cervical cancer. Therefore, these types were considered as 1A carcinogens. They all belong to the family of the α-Papillomaviridae, in particular to the species α5 (HPV51), α6 (HPV56), α7 (HPV18, HPV39, HPV45, HPV59) and α9 (HPV16, HPV31, HPV33, HPV35, HPV52, HPV58). Less evidence is available for a thirteenth type (HPV68, α7), which is classified as a 2A carcinogen (probably carcinogenic). Moreover, seven other phylogenetically related types (HPV26, HPV53, HPV66, HPV67, HPV68, HPV70 and HPV73) were identified as single HPV infections in certain rare cases of cervical cancer and were considered possibly carcinogenic (2B carcinogens). Recently, Halec et al [7] demonstrated that the molecular signature of HPV-induced carcinogenesis (presence of type-specific spliced E6*| mRNA; increased expression of p16; and decreased expression of cyclin D1, p53 and Rb) was similar in cervical cancers containing single infections with one of the eight afore-mentioned 2A or 2B carcinogens to those in cancers with single infections with group 1 carcinogens. Ninety six percent of cervical cancers are attributable to one of the 13 most common HPV types (groups 1 and 2A). Including the additional seven HPV types (group 2B) added 2.6%, to reach a total of 98.7% of all HPV-positive cervical cancers. From recently updated meta-analyses, it was shown that HPV68, HPV26, HPV66, HPV67, HPV73 and HPV82 were significantly more common in cancer cases than in women with normal cervical cytology, suggesting that for these HPV types, an upgrading of the carcinogen classification could be considered. However, there is no need to include them in HPV screening tests or vaccines, given their rarity in cervical cancers.

Keywords: biomarkers; carcinogenesis; cervical cancer; human papillomavirus.