HPV Types 16, 18, 45 and 31: The Most Important Oncogenic HPV Types Worldwide

Abstract

HPV infections are the most common sexually transmitted infections. HPV types differ in transmission capacity, virulence and in their ability to induce cancer. Over 90% of HPV-attributable cancers in women are cervical cancer. Most cancers of the uterine cervix are squamous cell carcinomas, while adenocarcinoma represents 10-12% of the global cervical cancer burden (in some countries of Europe and North America it amounts to over 20% of all invasive cervical cancer). On worldwide estimates, HPV-16 is consistently the most common type (60%) in cervical cancer, followed by HPV-18, -45 and -31. These four types combined account for approximately 80% of squamous cell carcinomas and 90% of adenocarcinomas. Some variability in the ranking thereafter has been described. Infections with HPV-16, -18, or -45 are associated with a higher risk for progression to cancer. The prognosis of HPV-16 and -18 is now being established by cohort studies with 10+ years of follow-up. The probability and time to progression to HSIL among HPV-16 and/or HPV-18 positive women with normal cytology is significantly higher than for any other of the high-risk HPV types, although the estimates for each individual type other than HPV-16 and -18 have not been firmly established. Adenocarcinoma is not detected effectively by cervical screening and is increasing in incidence in Europe and North America. It is associated with higher recurrence rates and poor outcomes. HPV-18 and -45 account for more than 40% of adenocarcinomas. Among other HPV positive cancer cases, HPV-16 is the dominant type. HPV-18 and-45 are the next most common types, although the relative role of the remaining HPV types is still to be determined. In summary, on a worldwide scale, prevention of cervical and other genital cancers would greatly benefit from vaccination focused on HPV-16 and -18.