Cervical intraepithelial neoplasia (CIN), also called cervical dysplasia, is an abnormal growth of cells on the surface of the cervix. This abnormal cervical growth can potentially lead to cervical cancer. CIN is classified into grades to describe the thickness of cervical abnormal cell growth. CIN is classified as CIN 1, CIN 2 ,and CIN 3 with increasing number designating the thickness of cervical lining with abnormal cells. The following is an overview of the CIN classification:
- CIN 1: Represents only mild dysplasia or abnormal cell growth. Usually indicates a mild infection with HPV and has high rate of regression to normal cells.
- CIN 2: Represents a mix of low- and high-grade abnormal growth or moderate dysplasia confined to the epithelium.
- CIN 3: Represents severe dysplasia with undifferentiated neoplastic cells involving more of the epithelium. This is considered precancerous and is often referred to as cervical carcinoma in situ.
Host immune response to the virus resolves most HPV lesions, especially genital condylomas and CIN 1 lesions. Neither of these is precancerous. This regression occasionally occurs with CIN 2, but rarely occurs with CIN 3. If the CIN does not regress, high-grade squamous intraepithelial lesions (HSIL) develop. HSIL may progress to invasive carcinoma, typically in older individuals.