Human papillomavirus (HPV) and cervical cancer
- Human papillomavirus (HPV) is a group of viruses that are extremely common worldwide.
- There are more than 100 types of HPV, of which at least 13 are cancer-causing (also known as high risk type).
- HPV is mainly transmitted through sexual contact and most people are infected with HPV shortly after the onset of sexual activity.
- Cervical cancer is caused by sexually acquired infection with certain types of HPV.
- Two HPV types (16 and 18) cause 70% of cervical cancers and precancerous cervical lesions.
- There is also evidence linking HPV with cancers of the anus, vulva, vagina and penis.
- Cervical cancer is the second most common cancer in women, with an estimated 530 000 new cases every year.
- Every year, more than 270 000 women die from cervical cancer; more than 85% of these deaths are in low- and middle-income countries.
- Vaccines against HPV 16 and 18 have been approved for use in many countries.
Human papillomavirus (HPV) is the most common viral infection of the reproductive tract. Most sexually active women and men will be infected at some point in their lives and some may be repeatedly infected.
The peak time for acquiring infection for both women and men is shortly after becoming sexually active. HPV is sexually transmitted, but penetrative sex is not required for transmission. Skin-to-skin genital contact is a well-recognized mode of transmission.
There are many types of HPV, and many do not cause problems. HPV infections usually clear up without any intervention within a few months after acquisition, and about 90% clear within two years. A small proportion of infections with certain types of HPV can persist and progress to cancer.
Cervical cancer is by far the most common HPV-related disease. Nearly all cases of cervical cancer can be attributable to HPV infection.
Though data on anogenital cancers other than cancer of the cervix are limited, there is an increasing body of evidence linking HPV with cancers of the anus, vulva, vagina, and penis. Although these cancers are less frequent than cancer of the cervix, their association with HPV make them potentially preventable using similar preventative strategies as those for cervical cancer.
Non-cancer causing types of HPV (especially types 6 and 11) can cause genital warts and respiratory papillomatosis (a disease in which tumours grow in the air passages leading from the nose and mouth into the lungs). Although these conditions very rarely result in death, they may cause significant occurrence of disease. Genital warts are very common and highly infectious.
Signs and symptoms
The majority of HPV infections do not cause symptoms or disease and resolve spontaneously. However, persistent infection with specific types of HPV (most frequently types 16 and 18) may lead to precancerous lesions. If untreated, these lesions may progress to cervical cancer, but this progression usually takes many years.
Symptoms of cervical cancer tend to appear only after the cancer has reached an advanced stage and may include:
- irregular, intermenstrual (between periods) or abnormal vaginal bleeding after sexual intercourse;
- back, leg or pelvic pain;
- fatigue, weight loss, loss of appetite;
- vaginal discomfort or odourous discharge; and
- a single swollen leg.
More severe symptoms may arise at advanced stages.
How HPV infection leads to cervical cancer
Although most HPV infections clear up on their own and most pre-cancerous lesions resolve spontaneously, there is a risk for all women that HPV infection may become chronic and pre-cancerous lesions progress to invasive cervical cancer.
It takes 15 to 20 years for cervical cancer to develop in women with normal immune systems. It can take only 5 to 10 years in women with weakened immune systems, such as those with untreated HIV infection.
Risk factors for HPV persistence and development of cervical cancer
- Early first sexual intercourse
- Multiple sexual partners
- Tobacco use
- Immune suppression (for example, HIV-infected individuals are at higher risk of HPV infection and are infected by a broader range of HPV types)
Scope of the problem
Cervical cancer is the second most frequent cancer in women in the world and the third greatest cause of death from cancer in women. Many more women die of cervical cancer in the developing world than in wealthier countries. Of the estimated more than 270 000 deaths from cervical cancer every year, more than 85% occur in developing countries.
In developed countries, programmes are in place which enable women to get screened, making most pre-cancerous lesions identifiable at stages when they can easily be treated. Early treatment prevents up to 80% of cervical cancers in these countries.
In developing countries, limited access to effective screening means that the disease is often not identified until it is further advanced and symptoms develop. In addition, prospects for treatment of such late-stage disease may be poor, resulting in a higher rate of death from cervical cancer in these countries.
The high mortality rate from cervical cancer globally (52%) could be reduced by effective screening and treatment programmes.
Screening for cervical cancer
Cervical cancer screening is testing for pre-cancer and cancer among women who have no symptoms and may feel perfectly healthy. When screening detects pre-cancerous lesions, these can easily be treated and cancer avoided. Screening can also detect cancer at an early stage and treatment has a high potential for cure.
Because pre-cancerous lesions take many years to develop, screening is recommended for every woman from aged 30 to 49 at least once in a lifetime and ideally more frequently. Screening is only effective if a high proportion of women participate.
Three different types of screening tests are currently available:
- conventional (Pap) test and liquid-based cytology (LBC)
- visual inspection with Acetic Acid (VIA)
- HPV testing for high-risk HPV types.
There are currently two vaccines which protect against both HPV 16 and 18, which are known to cause 70% of cervical cancers. The vaccines may also have some cross-protection against other less common HPV types which cause cervical cancer. One of the vaccines also protects against HPV types 6 and 11 which cause anogenital warts.
Clinical trial results show that both vaccines are safe and very effective in preventing infection with HPV 16 and 18.
Both vaccines work best if administered prior to exposure to HPV. Therefore, it is preferable to administer them before first sexual activity.
The vaccines cannot treat HPV infection or HPV-associated disease such as cancer.
Some countries have started to vaccinate boys as the vaccination prevents genital cancers in males as well as females, and one of the two available vaccines also prevents genital warts in males and females. WHO recommends vaccination for girls aged 9-13 years as this is the most cost-effective public health measure against cervical cancer.
HPV vaccination does not replace cervical cancer screening. In countries where HPV vaccine is introduced, screening programmes may still need to be developed or strengthened.
Cervical cancer prevention and control: A comprehensive approach
WHO recommends a comprehensive approach to cervical cancer prevention and control. The recommended set of actions includes interventions across the life course. It should be multidisciplinary, including components from community education, social mobilization, vaccination, screening, treatment and palliative care.
Primary prevention begins with HPV vaccination of girls aged 9-13 years, before they become sexually active.
Other recommended preventive interventions for boys and girls as appropriate are:
- warnings about tobacco use, which often starts during adolescence, and which is an important risk factor for cervical and other cancers;
- education about safe sexual practices, including delayed start of sexual activity;
- promotion and provision of condoms for those already engaged in sexual activity; and
- male circumcision.
Women who are sexually active should be screened for abnormal cervical cells and pre-cancerous lesions.
If treatment is needed to excise abnormal cells or lesions, cryotherapy (destroying abnormal tissue on the cervix by freezing it) is recommended.
If signs of cervical cancer are present, treatment options for invasive cancer include surgery, radiotherapy and chemotherapy.
WHO has developed guidance on how to prevent and control cervical cancer, including through vaccination and screening. The Organization works with countries and partners to develop and implement comprehensive programmes.
By the end of 2012, 45 countries had introduced HPV vaccination. Most of these are developed countries, but given that the global burden of cervical cancer falls heaviest on developing countries, there is still a great need for more countries to introduce the HPV vaccine as part of a national public health strategy that includes a comprehensive approach to prevention and control of cervical cancer.