Cervical intraepithelial neoplasia, or CIN, is the abnormal growth of precancerous cells in the cervix. Most cases of CIN stay the same or are eliminated by the host's immune system without intervention, but a small percentage of cases progress to become cervical cancer, usually cervical squamous cell carcinoma, or SCC (Agorastos et al., 2005). The major cause of CIN is infection with the sexually transmitted human papillomavirus (HPV), usually the high-risk HPV type 16.
CIN has four distinct grades: Grade I, or CIN1, the least risky type, represents only mild dysplasia, or abnormal cell growth (Agorastos et al., 2005) and is considered a low grade squamous intraepithelial lesion (LSIL; Park et al., 1998). Grades II and above, or CIN2+, considered high grade squamous intraepithelial lesions (HSIL; Park et al., 1998), show moderate dysplasia in CIN2, severe dysplasia in CIN3, and invasive carcinoma in CIN4 (Agorastos et al., 2005). Cases of CIN are thought by some to progress through these stages toward cancer in a linear fashion (Rapp and Chen, 1998; Agorastos et al., 2005; Hillemanns, 2005). However, evidence suggests that cancer can occur without first detectably progressing through these stages and that a high grade intraepithelial neoplasia can occur without first existing as a lower grade (Agorastos et al., 2005; Monnier-Benoit et al., 2005).
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