Abstract
1 min read<div>Abstract<p><b>Purpose:</b> Altered expression of cell cycle/apoptosis key regulators may promote tumor progression, reflect secondary genetic/epigenetic events, and impair the effectiveness of therapy. Their expression pattern might then identify gastrointestinal stromal tumor (GIST) patient subgroups with different response to imatinib and elucidate novel therapeutic targets.</p><p><b>Experimental Design:</b> Immunohistochemical evaluation of expression of p53, p16, p21, CHK2, CCND1, BCL2, CDK4, and MDM2 was done on 353 histologically validated GIST patients enrolled into a European/Australasian phase III trial. <i>TP53</i> was screened for mutations in cases with presumptive nonfunctional protein; that is, high p53 and low expression of the two downstream molecules p21 and MDM2. Results were correlated with clinicopathologic data, <i>KIT/PDGFRA</i> mutation status, and imatinib dosage.</p><p><b>Results:</b> Frequent impaired expression was found for BCL2 (78%), CHK2 (53%), p53 (50%), and p16 (47%). Stomach-originating GISTs showed significantly lower expression of p21, p16, and BCL2. <i>KIT/PDGFRA</i> wild-type GISTs had significant lower expression of CDK4. Eighty-eight percent of the high p53 expressers show low downstream target activation, indicating a nonfunctional p53 route. Of these high p53 expressers, 16.4% harbor a detectable <i>TP53</i> mutation. Multivariate analysis, including previously identified markers, showed an independent effect of p53 and p16 on progression-free survival (PFS). Patients with high level of CHK2 and p21 showed significantly better PFS upon a high-dose regimen.</p><p><b>Conclusions:</b> Impaired p53, p16, BCL2, and CHK2 expression is common in advanced GISTs. Distinct patterns of expression correlate with tumor site, genotype, and PFS. Cell cycle/apoptosis maintenance is instrumental for optimal response to imatinib.</p></div>
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