Proper Diagnostic Differentiation of Atypical Adenomatous Hyperplasia and Pulmonary Adenocarcinoma

Atypical adenomatous hyperplasia (AAH) is a precursor of lung adenocarcinoma. Pure AAH lesions often manifest as ground glass opacities on computed tomography (CT) scans, and are usually less than 5 mm in diameter. The histological diagnosis of AAH is often made with small biopsies, which raises doubts about the true nature of the whole lung lesion. We reported 4 patients presenting with a solitary pulmonary nodule greater than 5 mm in diameter and with an initial diagnosis of AAH based on CT-guided lung biopsies. Three of the patients who later received surgical resection or lung re-biopsy were ultimately diagnosed as having pulmonary adenocarcinoma. Further gene analyses revealed that all 3 patients with adenocarcinoma harbored epidermal growth factor receptor (EGFR) mutations. Differentiation between AAH and adenocarcinoma is clinically important, particularly with small biopsy specimens or when radiological images highlight the possibility of a more advanced disease status.