A 58-year-old woman undergoes lung cancer screening CT which reveals a 4 mm ground-glass nodule in the left upper lobe. Resection shows a small focus of atypical type II pneumocytes proliferating along pre-existing alveolar walls without invasion. What is the most appropriate diagnosis?

• A Adenocarcinoma in situ
• B Minimally invasive adenocarcinoma
• C Atypical adenomatous hyperplasia ✓
• D Lepidic predominant adenocarcinoma

Explanation

Atypical adenomatous hyperplasia (AAH) is a small pre-malignant lesion measuring ≤5 mm with atypical type II pneumocytes or Clara cells proliferating along alveolar walls. Adenocarcinoma in situ is defined as a lesion >5 mm but ≤3 cm with pure lepidic growth and no invasion. Minimally invasive adenocarcinoma has ≤5 mm of invasion. Lepidic predominant adenocarcinoma has >5 mm invasion or meets size criteria for invasive adenocarcinoma.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.