What is cervical intraepithelial neoplasia (CIN)?

Cervical intraepithelial neoplasia (CIN) is a precancerous condition in which abnormal cells grow on the surface of the cervix. The cervix is the opening between the vagina and the uterus in women. “Intraepithelial” means that the abnormal cells are present on the surface (epithelial tissue) of the cervix. The word “neoplasia” refers to the growth of new cells. Another name for CIN is cervical dysplasia.

It is important to remember that most people with CIN do not get cancer. If cancer does form, it takes years to develop, giving doctors time to find and remove problem areas.

What are the classifications of CIN?

Cervical intraepithelial neoplasia may be classified according to how much epithelial tissue is affected:

  • Low-grade neoplasia (CIN 1) refers to dysplasia that involves about one-third of the thickness of the epithelium.
  • CIN 2 refers to abnormal changes in about one-third to two-thirds of the epithelial layer.
  • CIN 3 (the most severe form) describes a condition that affects more than two-thirds of the epithelium.

How common is CIN?

About 250,000 to 1 million women in the U.S are diagnosed with CIN each year. The condition is found more often among women of childbearing age, particularly among women aged 25 to 35.

What are the symptoms of cervical intraepithelial neoplasia (CIN)?

CIN does not usually cause any symptoms. Abnormal cells are found only after a routine Pap smear.

What causes CIN?

CIN usually occurs after a woman becomes infected with the human papilloma virus (HPV). This is a virus that is spread through sexual contact. In many cases, the immune system by itself will get rid of the virus. There are over 100 strains of HPV. Some strains, such as HPV-16 and HPV-18, are more likely to infect the reproductive tract in women and cause CIN.

It is thought that more than 75% of women who are sexually active are infected with HPV at some point in time. About 50% of the HPV infections occur in women between the ages of 15 and 25. Most of the time, the infections go away with causing any permanent problems.

We do not know exactly why some women develop CIN after being infected with HPV. Some high-risk strains of HPV and the duration of the infection may play a role. Other risk factors include:

Factors that make the immune system weaker and raise the risk of HPV infections include:

  • Having sex with multiple partners
  • Becoming sexually active before age 18
  • Becoming infected with the human immunodeficiency virus (HIV)

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