CIN

Last edited 11/2020 and last reviewed 11/2020

Cervical intraepithelial neoplasia is the preinvasive stage of cervical cancer. It denotes atypical changes in the transformation zone - that part of the cervix in which exposed normal columnar epithelium is gradually replaced by normal squamous epithelium through metaplasia.

Metaplasia is enhanced by vaginal acidity and is most active during adolescence and the first pregnancy. The strong association between the development of malignancy with early sexual activity, and early age of first pregnancy is thought to be due to exposure of the transformation zone to carcinogens at times when it is most active and therefore, most vulnerable.

Cervical smear result

• for many women their abnormal result will show borderline changes or mild (low-grade) dyskaryosis. The areas of changed cells are known as cervical intraepithelial neoplasia, or CIN. CIN is graded on a scale of 1 to 3. Mild (low-grade) dyskaryosis is associated with the grade CIN 1
• Severe (high-grade) dyskaryosis is associated with CIN2 and CIN3

CIN is a histological diagnosis. It is important as:

• cytological changes in the transformation zone can be screened for and related to CIN
• treatment of CIN is relatively uncomplicated and curative
• low-grade CIN lesions rarely become invasive (1,2)
• risk of invasive cervical cancer is more than double that of the general population at least 10 years after treatment for cervical intraepithelial neoplasia grade 3 (3)
  • women are at an increased risk of invasive cervical cancer more than 25 years after treatment for cervical intraepithelial neoplasia grade 3
  • risk of invasive disease is noticeably increased in women aged more than 50 when treated
  • risk of vaginal cancer is increased in women treated for cervical intraepithelial neoplasia grade 3

Reference:

• (1) Ostor AG. Natural history of cervical intraepithelial neoplasia: a critical review. Int J Gynecol Pathol 1993;12: 186-92.
• (2) Holowaty P et al . The natural history of dysplasia of the uterine cervix. J Natl Cancer Inst 1999; 91: 252-58.
• (3) Strander B et al. Long term risk of invasive cancer after treatment for cervical intraepithelial neoplasia grade 3: population based cohort study.BMJ. 2007 Nov 24;335(7629):1077.