Cervical Cancer - Causes

Highlights	Symptoms	Treatment for Invasive Cervical Cancer
Introduction	Prevention	Resources
Causes	Diagnosis	References
Risk Factors	Treatment for CIN and Carcinoma in Situ
Prognosis	Treatment for Cervical Cancer

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. It should be noted, however, that most sexually active young women become infected with this virus, but only 10% remain infected for more than five years. Only those infected for longer than five years have a higher risk (about 50% above normal). Other factors are then needed to trigger the disease.

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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, 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 type 18 and HPV 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.