 About 50% of CIN 2 cases will regress within 2 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.