Immunohistochemical and molecular evaluation of the mdm-2 gene product in bronchogenic carcinoma

In this study, we investigated immunohistochemically the expression of mdm-2 protein in 93 surgically resected bronchogenic carcinomas. The findings were correlated with p53 protein detection status and clinicopathologic data (histologic type, differentiation grade of the lesions, lymph node metastases, and smoking history of the patients). Thirty of the 93 immunohistochemically examined specimens were subjected to Northern blot and differential polymerase chain reaction analysis to look into the mechanism of mdm-2 overexpression. Finally, we studied the concordance between p53 immunohistochemical positivity and p53 gene alterations as assessed by the single-strand conformation polymorphism technique. Seventy-three (78%) and 67 (72%) of 93 carcinomas showed nuclear immunoreactivity for mdm-2 and p53 proteins, respectively. We observed a high degree of concordance (75%) between p53 mutations and p53 immunolabelling, which was even higher in the specimens with p53 positively in more than 50% of the cells (90%). Despite the high percentage of mdm-2 and p53 expression, the two molecules were simultaneously detected in 50 (54%) of 93 cases. Forty-two (84%) of the 50 cases were accompanied by p53 mobility shifts, which indicated mutations. Interestingly, statistical analysis revealed an almost significant correlation between the carcinomas with mdm-2/p53 coexpression and lymph node disease (P = 0.058), which indicated a possible "gain of function" phenotype. In addition, absence of reactivity for both proteins was statistically more frequent in the patients without lymph node disease (P = 0.006). The mdm-2-positive/p53-negative immunohistochemical profile was more often seen in adenocarcinomas (P = 0.003), especially in well-differentiated ones (P = 0.02), than in other histologic types of lung cancer, which suggested a p53-independent pathway of mdm-2 overexpression. Molecular analysis showed that mdm-2 overexpression was a consequence of increased transcription rather than of mdm-2 gene amplification. The smoking history of the patients was strongly related to p53 (P = 10(-4)) even in the group of adenocarcinomas (P = 0.012). No correlation was observed between cigarette consumption and mdm-2 immunoreactivity.