Human Papillomavirus (HPV) is a common viral infection. Many HPV types exist, broadly categorized into low-risk and high-risk variants. Low-risk types typically cause benign growths, such as warts. High-risk HPV types can induce cellular changes that may lead to cancer over time. While HPV types 16 and 18 are widely recognized for their link to certain cancers, numerous other high-risk types are also significant. This article focuses on understanding these non-16/18 high-risk HPV types and what a positive test result for them indicates.
Understanding High-Risk HPV Beyond Types 16 and 18
While HPV 16 and 18 cause a substantial majority of cervical cancers, other high-risk types contribute to the remaining cases. These non-16/18 high-risk types include specific genotypes such as:
- HPV 31
- HPV 33
- HPV 35
- HPV 39
- HPV 45
- HPV 51
- HPV 52
- HPV 56
- HPV 58
- HPV 59
- HPV 66
- HPV 68
When the body’s immune system does not clear a high-risk HPV infection, its persistent presence can lead to chronic inflammation and genetic alterations within infected cells. This sustained viral presence can disrupt normal cellular regulation, potentially causing cells to become abnormal or precancerous. A positive test for any high-risk HPV type, even if not 16 or 18, indicates the presence of a virus with the capacity to contribute to cancer development.
Health Risks and Associated Cancers
Persistent infection with high-risk HPV types is a factor in the development of cervical cancer. While HPV 16 and 18 are responsible for approximately 70% of cervical cancer cases, other high-risk types account for a significant portion of the remaining cases globally. The progression to cancer involves viral DNA integrating into the host cell’s genome. This integration leads to the expression of viral proteins, particularly E6 and E7, which interfere with cellular regulatory mechanisms.
These viral proteins disrupt tumor suppressor genes like p53 and retinoblastoma protein (Rb), which normally control cell division and prevent uncontrolled growth. This interference can lead to the formation of precancerous lesions, often classified as cervical intraepithelial neoplasia (CIN) grades 2 or 3, or high-grade squamous intraepithelial lesions (HSIL). If these high-grade precancerous changes are not addressed, they can advance to invasive cervical cancer over several years.
Beyond cervical cancer, non-16/18 high-risk HPV types are also implicated in other anogenital cancers, including:
- Cancers of the anus
- Vulva
- Vagina
- Penis
Additionally, these other high-risk types play a role in a subset of oropharyngeal cancers, particularly those affecting the tonsils and base of the tongue.
Screening, Diagnosis, and Monitoring
Routine screening detects high-risk HPV infections and associated precancerous changes in the cervix. Cervical cancer screening often combines a Pap test, which examines cervical cells for abnormalities, with an HPV DNA test. The HPV DNA test identifies high-risk HPV types. Some tests differentiate between HPV 16/18 and other high-risk types, while others indicate “other high-risk HPV.”
A positive result for “other high-risk HPV” means one or more non-16/18 cancer-causing types are present. If a high-risk HPV test is positive, or a Pap test shows abnormal results, further evaluation is recommended. This often includes a colposcopy, a procedure using a magnified view to examine the cervix, vagina, and vulva for abnormal areas.
During colposcopy, biopsies may be taken from suspicious areas to determine the grade of cellular changes and confirm precancerous lesions. Regular monitoring follows, involving repeat Pap and HPV tests, or further colposcopic examinations. Monitoring ensures detected cellular changes do not progress, allowing for identification and treatment of precancerous conditions before they develop into invasive cancer.
Prevention Strategies
Vaccination is a primary strategy for preventing high-risk HPV infections. Current HPV vaccines, such as Gardasil 9, protect against nine HPV types:
- HPV 6
- HPV 11
- HPV 16
- HPV 18
- HPV 31
- HPV 33
- HPV 45
- HPV 52
- HPV 58
This broad coverage means the vaccine offers protection against the majority of high-risk types associated with cervical and other HPV-related cancers. Vaccination is effective when administered before potential exposure to the virus, typically in preteen years, but can still offer protection if given later.
Consistent and correct use of condoms can reduce the risk of HPV transmission. While condoms do not offer complete protection because HPV can infect areas not covered by a condom, studies show a reduction in risk with consistent use. Regular cervical cancer screening, including Pap tests and HPV DNA tests, serves as a secondary prevention method. These screenings enable early detection of high-risk HPV infections and precancerous lesions, allowing for timely intervention and treatment. Combining vaccination with routine screening and safer sexual behaviors can lower the risk of acquiring high-risk HPV infections and developing associated cancers.