October 25, 2014
   
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Human Papilloma Virus and Cervical Cancer
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Human Papilloma Virus and Cervical Cancer

 
Modern medicine's battle against cervical cancer is a tale of two worlds. In the developed world, it is a story of success. Thanks to Dr. George Papanicolaou's 1943 development of the Pap smear test, doctors can detect cellular changes that are precursors to cancer. If treated right away, these changes will not develop into cervical cancer. As a result, women who live in places where Pap smears are given regularly have seen their rates of cervical cancer plummet. From 1947 to 1982, for example, the incidence of cervical cancer among white American women fell by 75% and the death rate from cervical cancer by 80%.(1) Currently, about 80% of women in the U.S. take regular Pap smear tests.(2)

It is a different story in the developing world. Without the public health infrastructure to do cervical cancer screening or to evaluate Pap smear results, cervical cancer rates remain in the pre-1940s range. In many developing countries cervical cancer is still the most common cancer in women. Worldwide, there are 470,000 new cases and 230,000 deaths every year, compared to only 10,000 new cases and 3,700 deaths a year in the U.S.(3)

...[H]uman papilloma virus (HPV) plays a key role in cervical cancer. HPV is transmitted through sex and virtually all cases of cervical cancer begin with HPV infection.

In the past few decades, however, researchers have discovered that a virus called human papilloma virus (HPV) plays a key role in cervical cancer. HPV is transmitted through sex and virtually all cases of cervical cancer begin with HPV infection. The good news is that we can test for HPV infection. There is hope that the combination of the Pap smear test with the right kind of HPV test, plus the development of new vaccines to prevent HPV infection, will lead to new, dramatic advances in the fight against cervical cancer in every part of the world.

What Is Human Papilloma Virus?
HPV comes in many shapes and sizes. There are more than 100 known papilloma viruses that affect humans, so many that they are given numbers, such as HPV type 6 or type 16. Some HPV types cause skin warts. Over 40 types of HPV affect the genital tract, some causing genital warts. Others cause infections of the cervix.

Some types of HPV are strongly associated with a high risk of developing cervical cancer.(4)(6) Types 16 and 18 are known carcinogens and are found in 70% of American women with cervical cancer.(7)(8) Scientists believe that HPV initiates a process that leads, over time, to the development of cervical cancer; and that other factors, such as cigarette smoking, poor nutrition and infection with the sexually transmitted disease chlamydia, stimulate and lay the groundwork for cervical cancer.

How Women Get Genital HPV
Genital HPV is transmitted through sex. It is staggeringly common. Most sexually active young women will become infected, 40% within 16 months after first having vaginal sex. These infections can be with a succession of different HPV types or with more than one type at a time. The infections cause few or no symptoms and women — and men, for that matter — rarely realize that they have been infected. Most infections are completely destroyed by the body's immune system in a matter of months and do no long term harm.

Most sexually active young women will become infected, 40% within 16 months after first having vaginal sex.

A small number of infections, however — five to ten percent — survive and remain within the body and it is these that cause problems. The virus becomes incorporated into the genetic structure of the cervical cells, beginning a process that will eventually develop into precancerous cells. These are the same changes that are picked up by Pap smears. Left undetected and untreated, they can develop into cervical cancer. This persistent infection is called chronic HPV infection and is the most important risk factor for the development of cervical cancer.

Women are most likely to get a genital HPV infection in their 20s. As women age their risk goes down with the build up of immunity and more conservative sexual habits. Because it can take 10 to 15 years for HPV-related changes to become cancer, women infected in their 20s would not be expected to develop cervical cancer until their late 30s or 40s.

Other Risk Factors
Long before HPV's key role in cervical cancer was known, several other risk factors had been identified. The discovery of HPV has provided a common thread that links most of these factors:
  • Having sex at an early age: this is explained by the fact that in adolescents the immature cervical cells are much more vulnerable to HPV and other infections.
  • Multiple sex partners: there will be increased opportunities to contract more types of HPV.
  • Cigarette smoking: there are carcinogens in cigarette smoke that promote the development of cancer in the cervix and elsewhere.
  • Decreased immunity: women receiving immunosuppressive drugs and those with HIV/AIDS have a poor immune response to HPV.(9)(10)

Now that we know that HPV underlies most of these risk factors, it is clear that the key to cervical cancer prevention is identifying long-term HPV infection. After all, a woman could have many sexual partners, and many HPV infections, but if her body fights off these HPV infections and she never develops a chronic HPV infection, she would be at a very low risk of getting cervical cancer. On the other hand, a women with none of these risk factors, but who develops one chronic HPV infection, would be at a high risk.

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