RASSF1A gene inactivation in non-small cell lung cancer and its clinical implication

Methylation-associated inactivation of RASSF1, a putative tumor suppressor identified at 3p21.3, is reported in several cancers. We examined RASSF1 in non-small lung cancer (NSCLC) to search for clinical implications. RT-PCR analysis showed no expression of RASSF1A in 12 of 20 lung cancer cell lines. Loss of expression correlated well with promoter methylation status of these lines. Sequence analysis revealed 2 polymorphisms (codons 21 and 133) in RASSF1A transcripts, but not in RASSF1C transcripts. No somatic mutations were found. Of 7 cell lines with K-ros mutations at codon 12 or 6 1, 2 lost expression of RASSF1A, whereas in 13 cell lines with wild-type K-ras gene, 10 lost RASSF1A gene expression (p = 0.0521). We investigated methylation status of this putative tumor suppressor gene in 100 primary NSCLCs to determine whether there is a clinical significance. Forty-two of primary NSCLCs demonstrated methylated allele. There is no correlation between promoter methylation of RASSF1A and clinicopathological findings, including histological type or grade, tumor staging, p53 and K-ros mutational status, or patients' survival. In the cases of Stage I and II disease, however, RASSF1A methylation was associated with earlier recurrence (p = 0.0247). Epigenetic silencing of RASSF1A is a frequent event in non-small lung cancer and will provide novel opportunities to develop diagnosis and therapy of NSCLC. (C) 2003 Wiley-Liss, Inc.