Abstract: ObjectiveTo investigate the expression of p16INK4a protein in human cancers and analyze its clinical significance. 
MethodsA total of 642 cases surgical specimens of primary human tumors from 2014 to 2015 were underwent operations in the study. Immunohistochemical staining was used to detect and analyze the expression of p16INK4 in tumor tissues. 
ResultsOf the 642 tumor samples， 120 were benign and 522 were malignant. The expression rates of p16INK4a negative（-）， weak positive（+）， moderately positive（++） and strong positive（+++） were 1743％ （91／522）， 11.11％ （58／522）， 19.16％ （100／522） and 52.30％ （273／522） in malignant tumor tissues， respectively； while in benign lesions， the expression rates were 3417％ （41／120）， 2333％ （28／120）， 26.67％ （32／120） and 1583％ （19／120）， respectively. The difference was statistically significant （P＜0.05）. The positive expression rate of p16INK4a protein in different tissues derived tumors was not the same （P＜0.05）.Using p16INK4a protein as a biological molecules marker of malignant tumor， the sensitivity and specificity and positive predictive value of it were different as choosing different positive cell value. While using moderately positive as positive value， the sensitivity， specificity and positive predictive value were 71.46％， 57.50％ and 87.97％. While using strong positive as positive value， the sensitivity， specificity and positive predictive value were 52.30％，84.17％ and 93.49％. 
ConclusionThe compensatory high expression of p16INK4A is a tumor specific immune phenotype， which is related to the abnormal cell cycle patterns of tumor， and can be used as a molecular marker for the diagnosis， differential diagnosis and molecular typing of malignant tumors.

Key words: Malignant tumor, p16INK4a, Immunohistochemistry, Molecular target