Which HPV Warts Cause Cancer ?

In the United States, the most common sexually transmitted infection is Genital Human Papillomavirus (HPV). Since this disease is not reportable, the actual incidence is unknown but the estimated prevalence of genital HPV infection in the United States was 42.5% among adults age 18-69 between 2013-2014.^[1]

Of the hundreds of different HPV types, there are over 40 known strains or subtypes that infect the genital tract. Most infections remain undetected without symptoms and are cleared by the immune system within a few years. However, persistent infection can manifest as genital warts or cancer.^[2]

HPV Is Transmitted Through Sexual Contact

Transmission of HPV occurs through skin-to-skin contact, and the risk of contracting genital HPV is related to sexual activity. Risk factors include multiple sexual partners, sexual activity at an early age, history of previous sexually transmitted infections, a weakened immune system, smoking or having a partner with any of these risk factors. ^[3]

HPV and Cancer Risk

HPV types are divided into two types, “low-risk” and “high-risk”, depending upon whether or not they are associated with the development of cancer.

Low-risk HPV

The low-risk types of HPV are thought to be benign because although they may cause genital warts, they do not cause cancer. HPV types 6 and 11 are the most common and responsible for approximately 90% of genital warts.^[4]

High-risk HPV

The high-risk HPV types can cause precancers and cancers of the cervix (most common), vagina, vulva, anus, penis, and throat. HPV types 16, 18 are considered high-risk and responsible for over 70% of cervical cancer cases worldwide.^[5] Additional high-risk HPV types include 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 66, and 68.^[6]

What to Watch for with Genital Warts and Cancer

Genital warts appear as external growths on the vulva, anus, penis, or internally on the vagina or cervix. Genital warts can range from flesh-colored to reddish-brown, can appear alone or clustered together (like cauliflower), and can be raised or flat. The size of genital warts can vary as well, ranging from microscopic warts that you can barely see to large warts that can cause deformity. Most often genital warts cause no symptoms, but they can be itchy.

Confirmation of genital warts can be made with a physical examination. A biopsy of a growth can aid in the diagnosis but is typically not required.

Those infected with low-risk forms of HPV are also at a higher risk of being infected with high-risk HPV types and other sexually transmitted diseases.^[7,8]  

Physical examination should include a close inspection of the genital area for swollen lymph nodes, ulcerations, vesicles, and discharge. It is also important that all females follow the recommended screening guidelines for cervical cancer:

• Healthy women aged 21 to 65 years of age should get a Pap smear every three years
• Some women aged 30 to 65 can opt for a combination of a Pap smear and HPV testing every 5 years.

Reduce the Cancer Risk from Genital Warts

Genital warts are treatable, and there are many options to get rid of the growths. Most of the treatments are topical, some of which include the following.

• Imiquimod
• Podophyllotoxin
• Sinecatechins
• Cryotherapy
• Trichloroacetic acid
• Surgical removal (excision, laser, electrosurgery)

If a patient is being treated for genital warts and is unresponsive to treatment, it is possible that they may not have genital warts. The growth could potentially be something else which would require a biopsy of the growth to make the diagnosis.

HPV Testing 

The types of HPV that cause warts are not the same type as those that cause cancer. In a person infected with low-risk HPV types, it is possible for them to have a normal pap smear and HPV test. Typically, the HPV test is only performed during cervical cancer screening or as a follow-up measure in patients who have abnormal results on their pap smear.^[6] This test only looks for high-risk forms of the virus.

Testing for low-risk HPV types that cause genital warts is not recommended. In a research study that monitored over 35,000 women for up to 10.5 years, individuals who were positive for low-risk HPV types did not increase the risk of developing pre-cancerous lesions or cancer.^[4] Based on these results, authors believe that screening for low-risk HPV types can lead to unnecessary procedures, unwarranted psychological stress for patients, and wasted resources in addition to purposeless costs for the tests.^[4]

HPV Vaccine and Prevention of Genital Warts and Cervical Cancer

There are several HPV vaccines available that cover different HPV types.

The Bivalent HPV vaccine (Cervarix) prevents infection with high-risk HPV 16 and 18, the most common culprits implicated in the development of HPV-related cancers.^[6] 

Alternatively, the Gardasil vaccine has two formulations. The quadrivalent vaccine that prevents against HPV types 6, 11, 16 and 18, which include protection against the types associated with genital warts in addition to those associated with the development of cancer. The nonavalent vaccine covers against 6, 11, 16, 18, and the additional high-risk types also associated with cancers including 31, 33, 45, 52, and 58.^[9]

All of these vaccines are administered as a two or three-dose series at 0 and 6 months or 0, 2, and 6 months for both men and women. Vaccination against HPV is routine and recommended beginning at age 11 or 12. However, it may be given as early as age 9 years through age 26 years.