en Obstetrics & Gynicology Obstetrics & Gynicology Original Article Original Article <span style="font-size:14px;"><span style="font-family:Times New Roman;"><span style="line-height:14pt"><b><i><span style="color:blue">Background</span></i></b><i><span style="color:blue">:</span></i> the assessment of P16 expression and Ki-67 proliferative index is now proposed as an adjunct test for the diagnosis of high-risk precursor lesions for cervical cancer. The aim of the present study was to elucidate the quality expression of P16 and quantification Ki-67 index in different types of cervical intraepithelial neoplasia and also to determine the cutoff for Ki67 index to predict the severity of CIN lesions.<span style="font-size:9.0pt"></span></span><br> <span style="line-height:14pt"><b><i><span style="color:blue">Methods:</span></i></b> This cross-sectional study was conducted on patients with colposcopic indication. Selected samples with different CIN grades were examined for P16 and Ki-67 index by immunohistochemical (IHC) methods.<span style="font-size:10.0pt"></span></span><br> <span style="line-height:14pt"><b><i><span style="color:blue">Results:</span></i></b> All LSIL (CIN I) cases were negative for P16, while in 58.7% of HSIL cases (CIN 2/3), P16 was positive. The mean Ki67 index in the present study was 3.13 &plusmn; 2.65 in the upper two/third of the squamous epithelium in the LSIL group and 19.04 &plusmn;36.40 in the HSIL group, which was statistically significant. Also, the mean Ki67 index in full thickness squamous epithelium in HSIL group was significantly higher than LSIL. The sensitivity of P16 and Ki67 index in our study was 58.73%, 66.67% and the specificity was 100% and 100%, respectively.<b><i><span style="color:blue"></span></i></b></span><br> <span style="line-height:14pt"><b><i><span style="color:blue">Conclusion</span></i></b><i><span style="color:blue">:</span></i> Assessment of P16 expression and Ki67 index can be used to distinguish low grade (CIN1) intraepithelial lesion from high grade (CIN2/3) intraepithelial or precancerous lesions.<b><i><span style="color:#0033cc"></span></i></b></span></span></span> Ki 67 index, P16, Cervical Intraepithelial Neoplasia, High Grade Squamous Intraepithelial Lesion, Immunohistochemistry 69 75 http://caspjim.com/browse.php?a_code=A-10-2582-1&slc_lang=en&sid=1 Maryam Sadat Hosseini hoseiny339@yahoo.com 100319475328460040830 100319475328460040830 No Preventative Gynecology Research Center, Department of Obstetrics and Gynecology, Imam Hossein Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Maryam Talayeh m_talayeh@yahoo.com 100319475328460040831 100319475328460040831 Yes Department of Gynaeco-oncology, Imam Hossein Medical Center, Shahid Beheshti University of Medical, Tehran, Iran. Noushin Afshar Moghaddam afsharmoghadam@sbmu.ac.ir 100319475328460040832 100319475328460040832 No Professor of Pathology, Department of pathology, Imam Hossein Medical Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Maliheh Arab drmarab@yahoo.com 100319475328460040833 100319475328460040833 No Department of Gynaeco-oncology, Imam Hossein Medical Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Farah Farzaneh farahzaneh@yahoo.com 100319475328460040834 100319475328460040834 No Preventative Gynecology Research Center, Department of Obstetrics and Gynecology, Imam Hossein Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Tahereh Ashrafganjoei dr_ganjoei@hotmail.com 100319475328460040835 100319475328460040835 No Preventative Gynecology Research Center, Department of Obstetrics and Gynecology, Imam Hossein Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran.