Diagnosis: Mucinous adenocarcinoma (lepidic pattern)
• Mucinous adenocarcinomas can have a lepidic pattern with extracellular mucin;however, most cases also have stromal alteration and growth patterns of invasive adenocarcinoma.
• The majority of lepidic pattern mucinous adenocarcinomas harbor oncogenic KRAS mutations.
• The mucinous cells of congenital cystic pulmonary airway malformation, type I, are preneoplastic. This warrants removal of these malformations.
• Metastatic adenocarcinomas from the pancreas, biliary tree, and gastrointestinal tract can mimic lung primary lepidic mucinous adenocarcinoma. Such tumors can lead to diagnostic problems as the immunohistochemistry profile of lung lepidic mucinous adenocarcinoma can be TTF-1 negative and CK7 and CK20 positive.
• Nonmucinous adenocarcinoma in situ has the radiologic appearance of ground-glass opacity, but mucinous adenocarcinoma in situ and mucinous adenocarcinomas are more often solid by computed tomography scan.
