Cervical cancer
Description
An in-depth report on the causes, diagnosis, treatment, and prevention of cervical cancer.
Alternative Names
Dysplasia; Human papillomas virus; Pap smear
Causes
The human papillomavirus (HPV) has been detected in virtually all invasive cervical cancers and has been confirmed as the major cause of this cancer.
How HPV Is Transmitted.
HPV is spread primarily by having sex with an infected partner. Most sexually active young women become infected with this virus, but only 10% remain infected for more than 5 years. Only those infected for longer than 5 years have a higher risk (about 50% above normal). Other factors are then needed to trigger the disease.
How HPV Contributes to Cervical Cancer.
Researchers believe that most cervical cancers develop when various aggressive genetic HPV strains activate certain oncogenes (cancer-causing genes). Oncogenes called E6 and E7 are particularly important because they interfere with certain protective proteins, such as p53 and pRb, respectively. Under normal conditions, these proteins limit cell growth. Once they are blocked, cell growth can run rampant, leading to tumor development and cancer.
HPV Genetic Types.
More than 30 genetic variants of human papillomaviruses can be passed through sexual contact form one person to another. Their individual severity, however, varies widely according to genetic type. (Women initially infected by one type of HPV are still at risk for infection from other types.)
In women with CIN I dysplasia, the HPV viruses that are present are often types 6 and 11, which are low risk. Other low-risk HPV genetic types are 40, 42, 43, 44, 54, 61, 70, 72, and 81. These viral types often produce genital warts (condylomata) that rarely lead to cancer. (These warts usually affect the woman's genitals, the vagina, and vulva, rather than the cervix.)
Of the high-risk types, HPV types 18 and 16 have long been known to be particularly dangerous. These two genetic types and six others (31, 33, 35, 45, 52, and 58) account for 95% of HPV-related cervical cancers. Other high-risk types are 39, 51, 56, 59, 68, 73, and 82. All are associated with moderate dysplasia (CIN II) and carcinoma in situ (CIN III). Types 26, 53, and 66 are considered high-risk.
Severe HPV types have also been associated with an increased risk for other cancers, including other genital and lung cancers. The high-risk viruses generally produce flat and nearly invisible growths, compared to the usually harmless warts caused by low-risk HPV viruses.
Other Sexually Transmitted Diseases
Herpesviruses.
Certain herpesviruses (HSV), including HSV-6, HSV-2, HSV-7, and cytomegalovirus, have been detected in women with cervical cancer. HSV-6 is under particular suspicion for playing a role in activating the papillomavirus gene. The presence of these very common viruses, however, may simply be coincidental, and they may serve no purpose other than being bystanders.
Chlamydia Trachomatis.
Studies are finding an especially strong association between the incidence of
Chlamydia
trachomatis
, a sexually transmitted infection, and HPV. (
Chlamydia trachomatis
should not be confused with
Chlamydia pneumonia
e, a common cause of mild pneumonia in young adults.
Chlamydia pneumonia
e is not associated with cervical cancer.)
Other Sexually Transmitted Diseases.
Other sexually transmitted diseases that have been associated with cervical cancer include HIV and gonorrhea. These infections, however, also may only be markers of increased sexual activity and may not themselves cause cancer.
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Review Date: 9/1/2006
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Reviewed By: Harvey Simon, M.D., Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital.
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