The expression of the CD44 variant exon 6 is associated with lymph node metastasis in non-small cell lung cancer

Recently, it was suggested that splice variants of the surface glycoprotein CD44 (CD44v) were associated with tumor metastasis in some cancers. We examined the expression of variant forms of CD44 in 31 non-small cell lung carcinomas (NSCLCs) and in 8 normal lung tissue samples by reverse transcription-PCR (RT-PCR). CD44v3, CD44v5, CD44v6, and CD44v7 were not expressed or were weakly expressed in normal lung tissue (0 of 8). In contrast, CD44v3, CD44v5, CD44v6, or CD44v7 was expressed in 28 of 31 (90.3%) NSCLCs. Additionally, we examined the expression of CD44v6, which has been shown to be related to metastasis, in 5 normal lungs and 30 NSCLCs by RT-PCR and immunohistochemical analysis to clarify which cells express CD44v6 in NSCLC specimens. Thirty-six of 61 (59%) NSCLCs variably expressed CD44v6 by RT-PCR, and cancer cells were selectively immunostained by anti-CD44v6 antibodies in 23 of 30 (76.7%) NSCLCs. The results of immunohistochemical analysis almost correlated with those of RT-PCR. NSCLCs with lymph node metastasis expressed significantly more v6 exon than did those without lymph node metastasis [23 of 29 (79.3%) versus 13 of 32 (40.6%); P < 0.01]. There was a significant association between the intensity of v6 expression by RT-PCR and the frequency of cases showing lymph node metastasis (Cochran-Armitage's test, P < 0.002). In conclusion, this study demonstrated that in NSCLC, a number of variant forms of CD44 are frequently expressed, although these variants are infrequently expressed in normal lung tissue, and that the expression of CD44v6 is particularly associated with lymph node metastasis in NSCLC.