RESUMO
<p><b>OBJECTIVE</b>To study the methylation status of P16 gene promoter and the expression of P16 protein in gastrointestinal stromal tumors(GIST) and to explore the prognostic value.</p><p><b>METHODS</b>Methylation status of the P16 promoter was detected by methylation- specific polymerase chain reaction (MSP) and the expression of P16 protein by immunohistochemistry in 62 patients with GIST.</p><p><b>RESULTS</b>The status of P16 gene methylation and the expression of P16 protein were significantly different among the patients with different subclassification of GIST using Fletcher's scheme (P < 0.05, P < 0.01). And there were significant differences in progressive disease (PD) among various levels of P16 expression (P < 0.01). P16 gene methylation was closely related to P16 protein. P16 gene methylation accounted for 75% in the tumor tissue with less than 50% P16 positive cells, and accounted for only 10% in the tumor tissue with more than 50% P16 positive cells (P< 0.01).</p><p><b>CONCLUSION</b>P16 immunohistochemical assessment can be used as a prognostic index for GIST. The patients with more than 50% fraction of cells with low P16 immunostaining have poor prognosis.</p>