Cervical intraepithelial neoplasia
Cervical intraepithelial neoplasia (CIN), also known as cervical dysplasia, is the abnormal growth of cells on the surface of the cervix that could potentially lead to cervical cancer.[1] More specifically, CIN refers to the potentially precancerous transformation of cells of the cervix.
Cervical intraepithelial neoplasia
Cervical dysplasia
CIN most commonly occurs at the squamocolumnar junction of the cervix, a transitional area between the squamous epithelium of the vagina and the columnar epithelium of the endocervix.[2] It can also occur in vaginal walls and vulvar epithelium. CIN is graded on a 1–3 scale, with 3 being the most abnormal (see classification section below).
Human papillomavirus (HPV) infection is necessary for the development of CIN, but not all with this infection develop cervical cancer.[3] Many women with HPV infection never develop CIN or cervical cancer. Typically, HPV resolves on its own.[4] However, those with an HPV infection that lasts more than one or two years have a higher risk of developing a higher grade of CIN.[5]
Like other intraepithelial neoplasias, CIN is not cancer and is usually curable.[3] Most cases of CIN either remain stable or are eliminated by the person's immune system without need for intervention. However, a small percentage of cases progress to cervical cancer, typically cervical squamous cell carcinoma (SCC), if left untreated.[6]
There are no specific symptoms of CIN alone.
Generally, signs and symptoms of cervical cancer include:[7]
HPV infection of the vulva and vagina can cause genital warts or be asymptomatic.
The cause of CIN is chronic infection of the cervix with HPV, especially infection with high-risk HPV types 16 or 18. It is thought that the high-risk HPV infections have the ability to inactivate tumor suppressor genes such as the p53 gene and the RB gene, thus allowing the infected cells to grow unchecked and accumulate successive mutations, eventually leading to cancer.[1]
Some groups of women have been found to be at a higher risk of developing CIN:[1][8]
Additionally, a number of risk factors have been shown to increase an individual's likelihood of developing CIN 3/carcinoma in situ (see below):[9]
Outcomes[edit]
It used to be thought that cases of CIN progressed through grades 1–3 toward cancer in a linear fashion.[29][30][31]
However most CIN spontaneously regress. Left untreated, about 70% of CIN 1 will regress within one year; 90% will regress within two years.[32] About 50% of CIN 2 cases will regress within two years without treatment.
Progression to cervical carcinoma in situ (CIS) occurs in approximately 11% of CIN 1 and 22% of CIN 2 cases. Progression to invasive cancer occurs in approximately 1% of CIN 1, 5% of CIN 2, and at least 12% of CIN 3 cases.[3]
Progression to cancer typically takes 15 years with a range of 3 to 40 years. Also, evidence suggests that cancer can occur without first detectably progressing through CIN grades and that a high-grade intraepithelial neoplasia can occur without first existing as a lower grade.[1][29][33]
Research suggests that treatment does not affect the chances of getting pregnant but it is associated with an increased risk of miscarriage in the second trimester.[34]
Epidemiology[edit]
Between 250,000 and 1 million American women are diagnosed with CIN annually. Women can develop CIN at any age but women generally develop it between the ages of 25 and 35.[1] The estimated annual incidence of CIN in the United States among persons who undergo screening is 4% for CIN 1 and 5% for CIN 2 and CIN 3.[35]