“…Although K-ras mutations have been frequently found in lung tumours, the timing of their occurrence in the multistep process of lung carcinogenesis remains poorly understood. Such studies used tissue specimens removed at biopsy or resection (Sugio et al, 1992;Westra et al, 1993;Clements et al, 1995;Yakubovskaya et al, 1995;Urban et al, 1996;Keohavong et al, 1997b;Urban et al, 2000), and cell samples microdissected from embedded lung tissue sections (Sugio et al, 1994;Westra et al, 1996). Taken Topographic analysis of K-ras mutations in histologically normal lung tissues and tumours of lung cancer patients together, some of these studies suggest that K-ras mutations occur relatively late in lung cancer development (Sugio et al, 1994;Yakubovskaya et al, 1995;Urban et al, 1996), while other studies indicate that they could represent early events in this process (Li et al, 1994;Clements et al, 1995;Keohavong et al, 1997b;Urban et al, 2000).…”