Some epithelial cells are prone to abnormal growth or dysplasia, which can progress to precancerous growth called neoplasia. Early neoplastic growth is often reversible and does not always result in cancer. 

Under certain abnormal conditions, one type of epithelial tissue may undergo transformation into another type in another reversible process called metaplasia. In heavy cigarette smokers, the ciliated pseudostratified epithelium lining the bronchi can be transformed into stratified squamous epithelium.