The four major histological types of lung cancer are adenocarcinoma, squamous 
cell carcinoma (SQ), large cell carcinoma and small cell carcinoma. Over the 
past few decades, the incidence of lung adenocarcinoma has increased gradually 
in most countries as the most frequently occurring histological type, displacing 
SQ. Adenocarcinoma is the predominant type of lung cancer among lifelong 
non-smokers and among females. Especially in East Asian countries, the cause(s) 
of the increase in adenocarcinomas are not clear. Several genetic mutations 
specific to lung adenocarcinomas have been found, representing attractive 
targets for molecular therapy. Recently, the pathological classification of lung 
adenocarcinoma was revised by integrating the newer clinical and biological 
knowledge concerning this prevailing type. Additional epidemiological, 
pathological and genetic studies are required to better understand this type of 
lung cancer.