How does the k-ras gene cause lung cancer?

One step: When k-ras takes a mutation that makes it stuck on the "on" position, it confers an unfair growth advantage on the cell and its progeny. Kras mutated lung cancers tend to occur in smokers and make mucin. There's no medicine right now that works especially well for this subcategory of cancers and its presence suggests other good target mutations are probably not present. Good luck, stay proactive.