Human Papillomavirus (HPV) is the most frequent sexually transmitted infection globally, often transmitted through intimate skin-to-skin contact. Most people contract HPV at some point, and the immune system usually clears the virus naturally within one to two years without causing health issues. However, certain persistent strains can lead to cellular changes. Screening tests are designed to detect these specific types. A positive result means a strain has been identified, often followed by genotyping to determine the exact type present.
Understanding High-Risk HPV Genotypes
HPV types are categorized by genotype and classified into low-risk and high-risk groups based on their potential to cause disease. Low-risk types, such as HPV 6 and 11, typically cause external changes like genital warts and rarely lead to cancer. High-risk genotypes, which include about a dozen types, are capable of causing long-term cellular changes that can lead to cancer.
Types 16, 18, and 45 are specifically flagged in screening because they represent the most aggressive high-risk types. HPV 16 is the most prevalent, accounting for the largest percentage of HPV-related cancers globally. A positive test for any of these three types signals a need for closer monitoring due to their high propensity for causing precancerous lesions.
The Specific Cancer Risk Associated with Types 16, 18, and 45
A persistent infection with high-risk HPV types 16, 18, and 45 can lead to precancerous lesions known as dysplasia. This occurs when viral proteins interfere with the normal growth regulation of host cells, causing abnormal growth. If these changes, such as cervical intraepithelial neoplasia (CIN), are left untreated, they can progress over many years into invasive cancer. Types 16 and 18 alone cause approximately 70% of all invasive cervical cancer cases. HPV 45 is the third most carcinogenic type and is often associated with adenocarcinoma, a form of cervical cancer originating in glandular cells that can be harder to detect.
Beyond the cervix, these high-risk types are linked to several other cancers affecting both men and women. These associated cancers include anal, vaginal, vulvar, penile, and oropharyngeal cancers, which affect the back of the throat, tonsils, and base of the tongue. HPV 16 is a major contributor to cancers of the anus and the oropharynx.
Medical Follow-Up After a Positive Result
A positive result for HPV 16, 18, or 45 does not mean cancer is present, but it requires immediate and structured follow-up care. Due to the elevated risk, guidelines recommend a more intensive surveillance plan than for other high-risk HPV types. The standard next step is usually a colposcopy, where a healthcare provider examines the cervix, vagina, and vulva using a specialized magnifying instrument.
During the colposcopy, the physician applies a solution to highlight areas of abnormal cell growth (dysplasia). If abnormal tissue is identified, a small sample (biopsy) is collected for laboratory analysis to determine the severity of cellular changes. Management focuses on detecting and treating precancerous changes before they progress to cancer. For example, a positive result for HPV 16 often leads to an immediate colposcopy referral, even if the Pap smear is normal. Adhering to the monitoring schedule set by the healthcare provider is the most effective way to prevent cancer development.