A 65-year-old smoker with a 3 cm peripheral lung nodule undergoes resection. Histology shows tumour cells forming glands with apical mucin, some with hobnail morphology, growing lepidically along alveolar walls without stromal invasion, vascular invasion or pleural involvement. Maximum invasive component is 4 mm. According to the 2021 WHO lung tumor classification, what is the correct diagnosis?
- A Minimally invasive adenocarcinoma (MIA) — invasive component ≤5 mm, predominantly lepidic pattern, carries a near 100% disease-specific 5-year survival after complete resection ✓
- B Adenocarcinoma in situ (AIS) — purely lepidic growth without any invasion; complete resection is curative
- C Invasive adenocarcinoma, lepidic predominant — based on the >5 mm lepidic-pattern background
- D Atypical adenomatous hyperplasia (AAH) — precursor lesion <5 mm with mild cytological atypia
Explanation
The 2021 WHO classification defines minimally invasive adenocarcinoma (MIA) as a solitary, small (≤3 cm) adenocarcinoma with predominantly lepidic pattern and a single focus of invasion ≤5 mm. The invasion criteria include: stromal invasion, vascular invasion, pleural involvement, and invasive components (acinar, papillary, micropapillary, solid, or enteric patterns). This lesion has 4 mm of invasion = ≤5 mm, meeting MIA criteria. MIA carries near-100% 5-year survival with complete resection (sublobar or lobar). AIS has NO invasion whatsoever. Invasive adenocarcinoma, lepidic predominant requires invasion >5 mm. AAH is a ≤5 mm atypical/hyperplastic focus without the defined adenocarcinoma criteria.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.