Novel staging protocol for non-small-cell lung cancers according to MRP-1/CD9 and KAI1/CD82 gene expression

The transmembrane-4 superfamily (TM4SF) is a recently discovered family of genes. Of the TM4SF members, MRP-1/CD9, KAI1/CD82, and ME491/CD63 have been reported to modulate tumor progression or metastasis. In this study, we investigated the relationships between these three genes, MRP-1, KAI1, and ME491, in patients with non-small-cell lung cancers (NSCLCs). Moreover, we assessed the prognostic value of evaluating the expressions of MRP-1, KAI1, and ME491 simultaneously in NSCLCs.

One hundred seventy-two patients up to stage IIIB NSCLC underwent radical surgery during the period of January 1991 through June 1994. Using a quantitative reverse-transcriptase polymerase chain reaction (RT-PCR) analysis, we studied the expression of MRP-1, KAI1, and ME491 genes in these patients.

We found that 109 patients (63.4%) had MRP-1-positive tumors and 42 patients (24.4%) had KAl1-positive tumors. Conversely, all 172 patients expressed ME491. No relationship was found between MRP-1 expression and KAI1 expression. We classified these patients into three groups. The 36 patients who were positive for both MRP-1 and KAI1 were defined as group A; the 79 patients with reduced expression of either MRP-1 or KAI1 were defined as group B, and the remaining 57 patients with reduced expression of both MRP-1 and KAI1 were defined as group C. This new classification was correlated with nodal status, tumor status, and pathologic stage (P = .0056, P = .0003, and P < .0001, respectively). In NSCLC patients, the 5-year survival rate of group A patients was significantly better than that of group B patients and much better than that of group C patients (86.8%, 53.9%, and 31.5%, respectively; P < .0001). Cox multivariate regression analysis showed that this new classification in NSCLCs was a significant prognostic factor, as was the nodal status (P < .0001).

Our results suggest that a low MRP-1 and KAI1 expression by tumors of the lung may be associated with poor prognosis. It is conceivable that the evaluation for MRP-1 and KAI1 expression may identify node-negative lung cancer patients who are at high risk for early disease recurrence, and thus need intensive adjuvant therapy.