To reveal the adenocarcinomatous lineage of the solid variant, demonstration of intracellular mucin production may be performed. Foci of squamous metaplasia and dysplasia may be present in the epithelium proximal to adenocarcinomas, but these are not the precursor lesions for this tumor. Rather, the precursor of peripheral adenocarcinomas has been termed atypical adenomatous hyperplasia (AAH).[8] Microscopically, AAH is a well-demarcated focus of epithelial proliferation, containing cuboidal to low-columnar cells resembling club cells or type II pneumocytes.[8] These demonstrate various degrees of cytologic atypia, including hyperchromasia, pleomorphism, prominent nucleoli.[8] However, the atypia is not to the extent as seen in frank adenocarcinomas.[8] Lesions of AAH are monoclonal, and they share many of the molecular aberrations (like KRAS mutations) that are associated with adenocarcinomas.[8]