Caveolin-1, a 21-to 24-kd protein, is the principal component of caveolae, which are special invaginated microdomains of the plasma membrane present in most mammalian cells. 1 It is well established that caveolin-1 is a tumor suppressor gene. Caveolin-1 mRNA and protein expression are frequently lost in human cancer cell lines. Re-expression of caveolin-1 in oncogenically transformed cell lines inhibits tumor cell growth and reduces tumorigenicity. [2][3][4][5][6] Several mechanisms have been proposed for caveolin-1 to function as a tumor suppressor. Caveolin-1 may exert its tumor-growth inhibition by contact inactivation of signaling molecules such as v-src, Ha-Ras, protein kinase A, PKC, and p42/44 MAP kinase within caveolae. [7][8][9][10] In addition, down-regulation of caveolin-1 in colon carcinoma cells has been shown to prevent the degradation of inducible nitric oxide synthase via the proteosome pathway, which, in turn, increases the local nitric oxide concentration to facilitate tumorigenesis. 11 Caveolin-1 can also function as a tumor metastasispromoting molecule, which is unrelated to its obvious function of cell growth inhibition. 12 Elevated expression of caveolin-1 is found to be associated with progression of prostate, colon, and breast carcinoma. 13,14 Inhibition of c-myc-induced apoptosis by caveolin-1 was recently proposed to promote progression of prostate cancer, 15 and it may serve as a prognostic indicator for these patients. 16 Nonetheless, it still remains unclear whether and how caveolin-1 can potentiate tumor progression in other types of human cancer.In the present study, we investigated the expression pattern of caveolin-1 both in a series of lung carcinoma cell lines (CLs) with varying invasive/metastatic ability 17