A 62-year-old male ex-smoker is found to have a 2.2 cm pure ground-glass opacity (GGO) nodule in the right upper lobe. CT-guided biopsy shows atypical pneumocyte proliferation along alveolar septa with no stromal, vascular, or pleural invasion. The current WHO 2021 lung tumour classification designation for this lesion, if the lesion is entirely GGO with pure lepidic growth and no invasion, is:

• A Minimally invasive adenocarcinoma (MIA) — if ≤3 cm with ≤5 mm invasive component
• B Lepidic-predominant adenocarcinoma — if >3 cm regardless of invasive component
• C Adenocarcinoma in situ (AIS) — if ≤3 cm, pure lepidic, no invasion ✓
• D Atypical adenomatous hyperplasia (AAH) — if ≤0.5 cm with lepidic growth

Explanation

The WHO 2021 lung tumour classification retains the preinvasive hierarchy for pulmonary adenocarcinoma: Atypical adenomatous hyperplasia (AAH) — ≤0.5 cm, minimal cytological atypia; Adenocarcinoma in situ (AIS) — ≤3 cm, pure lepidic growth along intact alveolar septa using pre-existing alveolar walls as scaffold, NO stromal/vascular/pleural/alveolar invasion, no intraluminal mucin or solid component; Minimally invasive adenocarcinoma (MIA) — ≤3 cm lepidic-predominant adenocarcinoma with ≤5 mm invasive component. AIS and MIA both carry near-100% 5-year disease-free survival after complete resection. The 2.2 cm lesion described with pure lepidic growth and no invasion fits AIS. If invasion were present at ≤5 mm, it would be MIA.

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

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Written and medically reviewed by the StethoPrep medical team.