Infectious Diseases

Hpv and Cervical Cancer



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The human papillomavirus (HPV) is a sexually transmitted virus associated with the development of cervical cancers and genital warts. There are many strains of HPV: HPV-16 is the most oncogenic (cancer causing) strain causing approximately 50% of cervical cancers. Other oncogenic strains that are associated with about 30% more cases of cancers harboring virus particles are HPV-18, 31, 33, and 45.

Though women under the age of 20 have a higher occurrence of infection with multiple strains of HPV, a 2001 study found that the incidence of cervical cancer is not any higher under those conditions than in women infected with only a single strain. A study of Brazilian women found that about 70% of women (958 out of almost 1500 women), with an average age of 33 years, did not have any HPV infection over the course of the 12 month study. Half of the women who did have an infection at some point only had it at one visit and had cleared it by the next visit 4 months later. This is further evidence of what was known about most HPV infections being self-limiting. Cervical cancer is known to be caused by cellular alterations caused by persistent HPV infection with a single strain.

There are approximately 11,000 women diagnosed with cervical cancer each year in the U.S. and more than 3,500 deaths are associated with the cancer each year. After the development of the Pap smear in the 1950s, the rate of cervical cancer decreased by 74% according to the American Cancer Society. The rate of cervical cancer still decreases by approximately 4% a year because of better treatments, detection, and education. Risk factors for the development of cervical cancer include the use of oral contraceptives, smoking, early sexual encounters, multiple sexual partners, and viruses.

According to the American Cancer Society, cervical cancer rarely affects women under the age of 20 and the common ages for infection are between 35 and 55 years. Also, nearly 20% of patients who are diagnosed with cervical cancer are over the age of 65. Cervical cancer is one of the more treatable cancers, the 5-year relative survival rate for the earliest stage of invasive cervical cancer is 92% and the overall rate is about 72%.

Cervical cancer often does not exhibit any symptoms until the advanced stages. Pain and vaginal bleeding may be observed. Vaginal bleeding after menopause is abnormal and medical advice should be sought. The earliest stages of cancer development can be detected by a Pap smear (Papanicolaou test) which is done by gynecologists during a regular pelvic exam to determine if any changes have occurred in the cervical epithelium, an indicator of cancer development.

A cervical biopsy confirms a diagnosis of cervical cancer. A tissue sample is obtained by a specialist in a gynecologist's office or by the LEEP technique, an electrified loop, which is sometimes done as a cone biopsy in an operating room. There are also HPV tests available to determine clinically whether a woman has been infected with oncogenic strains. An alternative to a Pap smear is a colposcopy, a pelvic examination done with a small microscope used to observe the cervix at 8-10 times magnification.

Once cervical cancer is diagnosed treatment consists of preventing the precancerous cells from becoming cancerous and invasive. Removal of the cells during biopsy sometimes is enough. Other times more invasive surgical procedures are necessary. X-rays and other diagnostic techniques are used to gauge the spread of the cancer. Removal of tissues, cryosurgery, laser surgery, and cauterization are all available options depending on the extent of the cancer and the individual conditions of each patient.

In 2006 the FDA approved a vaccine for cervical cancer, but when all the factors are taken into account, only a small proportion of women benefit from the Gardasil vaccine. Studies have shown that approximately 5% of women will have persistent HPV infections, the causative agent for HPV-associated cancers. Limiting sexual partners and sexual contact can prevent HPV infection. Other risk factors can also be limited and prevent some infections. Regular pelvic exams and Pap smears are still the best intervention.

Reference

Rousseau, M.C. et al., 2001. Cervical coinfection with human papillomavirus (HPV) types as a predictor of acquisition and persistence of HPV infection. The Journal of infectious diseases, 184(12), p.1508-17.

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