Human papilloma viruses (HPV) are a large group of related viruses, some of which play a part in the development of cervical epithelial cancers. HPV is also associated with skin cancer, cancers of the mouth, and anal cancers.
More recently, it has been suggested that HPV may be associated with an increased risk of lung cancer. In addition, a group of researchers at a cancer research center in Seattle reported in 2004 that smoking appears to increase the risk of anal cancer in women as well as men infected with HPV who practice anal sex.
The family of human papilloma viruses includes a large number of genetically related viruses. Many of these cause warts, including the warts commonly found on the skin. Another group of HPV preferentially infect the mucosal surfaces of the genitals, including the penis, vagina, vulva, and cervix. These are spread among adults by sexual contact. One group of HPV that infect the genitals causes soft warts often designated condylomata acuminata.
These genital warts are quite common and rarely if ever become cancerous. The most common of these low-risk HPV types are designated HPV 6 and 11. The second group of viruses, termed high-risk HPV types, is associated with the development of cervical cancer. Individuals infected with these viruses are at higher risk for the development of precancerous lesions. Typically, infection with these viruses is common in adolescents and women in their twenties, and usually do not result in cancerous growth.
The most common high-risk HPV is type 16. The appearance of abnormal cells containing high-risk HPV types is seen most frequently in women over the age of 30 who have abnormal Pap smears.
It is possible that other viruses work together with human papilloma viruses to produce precancerous changes in tissue. Cases of tongue cancer have been reported in which HPV was found together with Epstein-Barr virus, or EBV.
HPV infections are very common. At some point in their lives, greater than 75% of people are infected with HPV, making HPV the most common sexually transmitted disease. According to the Centers for Disease Control and Prevention (CDC), 20 million Americans are infected with HPV as of 2004, with 6.2 million new cases occurring each year.
In general, HPV infections do not cause any obvious symptoms, which increases the likelihood of sexual transmission. Genital warts will occur in 1 or 2 of every 100 people. Abnormal Pap smears with atypical cells due to HPV can occur in 2-5% of women. If untreated, these women are at increased risk to develop cervical cancer. Virtually all cases of cervical cancer involve high-risk HPV types. It is believed that most cervical cancers take about five years to progress from early cellular changes to an invasive, life-threatening cervical cancer. It is not fully understood why most infections with high-risk HPV are of short duration, while a small percentage persist and eventually transform cervical cells to a state of cancerous growth.
In addition to producing precancerous lesions in some patients, HPV infections in women are a health concern because they can be transmitted to the respiratory tract of a baby during childbirth. This type of HPV infection may lead to juvenile-onset recurrent respiratory papillomatosis (JO-RRP), in which papillomas or warts form in the child’s airway, producing hoarseness or partial blockage of the windpipe. As of 2004, surgery is the usual treatment for JO-RRP, but the warts often recur and require additional surgery to remove them. Cidofovir and interferon are often given as adjuvant treatments for this disease as of the early 2000s. JO-RRP is a serious illness, leading to death in a significant number of affected children.
The relationship among HPV, precancerous cellular changes, and cervical cancer have led to the suggestion that testing for the presence of HPV can be a useful addition to Pap smears. Pap smears involve microscopic analysis of cells removed from the cervix. The results of these tests are generally reported as normal, or consistent with the presence of cancer or a precancerous condition. Patients receiving the latter diagnosis usually are treated, either by excisional or ablative therapy surgery or some other means, in order to remove the tumor or precancerous lesion. In some cases the cytologist or pathologist examining a Pap smear reports a “borderline” result when abnormal cells are observed, but it is not possible to distinguish whether the changes seen are due to early precancerous changes, or inflammation caused by some infectious agent or irritant. In these cases, some physicians and scientists believe that testing for the presence of HPV can help to identify those women who should be closely followed for the development of early cancerous lesions, or who should undergo colposcopy, a procedure to examine the cervix for precancerous lesions. These cancer precursors, termed cervical intraepithelial neoplasia (CIN) when identified early, before they have become invasive, can almost always be completely removed by minor surgery, essentially curing the patient before the cancer has had a chance to develop. The cervical tissue removed, which includes the precancerous tissue, is examined as part of a biopsy to confirm the diagnosis, and if requested by a doctor, can be tested for the presence of high-risk HPV types. This does not occur often.
Treatments
The only accepted treatment for HPV-related lesions is removal or eradication by surgery, lasers, cryotherapy, or electrocauterization. Since the incidence of latent and recurrent infections is high, the eradication of HPV is not always 100% effective. It is essential to be aware that HPV is a sexually transmitted disease and women must engage in safe sex practices to decrease the risk of spreading the virus or becoming re-infected. The development of an HPV vaccine that would render individuals resistant to infection by at least some of the high-risk HPV types is a matter of considerable interest. It is possible that such a vaccine will be available by 2010. As of 2004, a phase I study of a vaccine for HPV type 18, which causes 70% of cervical cancers, is under way at the University of Iowa.
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