Atypical adenomatous hyperplasia (AAH) is an hyperplastic lesion of the epithelial lining of pulmonary alveoli.
Tumorigenesis
A multi-step carcinogenesis hypothesis suggests a progression from atypical adenomatous hyperplasia (AAH) through bronchioalveolar carcinoma (BAC) to invasive adenocarcinoma (AC), but to date this has not been formally demonstrated.
References
Pulmonary atypical adenomatous hyperplasia Wikipedia(Text) CC BY-SA