A 60-year-old smoker has a peripheral lung adenocarcinoma with the WHO 2021 classification pattern that shows atypical cells growing along pre-existing alveolar walls without stromal, vascular, or pleural invasion and without central fibrosis. This histological pattern is classified as:
- A Adenocarcinoma in situ (AIS) — pure lepidic growth, ≤3 cm, 100% 5-yr DSS if completely resected ✓
- B Minimally invasive adenocarcinoma (MIA) — invasive focus ≤5 mm
- C Lepidic predominant adenocarcinoma — invasive component present but lepidic is the dominant pattern
- D Acinar predominant adenocarcinoma — mimicking alveolar architecture
Explanation
Adenocarcinoma in situ (AIS) is defined by the WHO 2021 classification as a ≤3 cm adenocarcinoma with pure lepidic growth pattern — atypical pneumocytes (type II or Clara cell-like) growing along intact alveolar walls without any stromal, vascular, or pleural invasion and without intraluminal tumor or central fibrosis. It has near-100% disease-specific survival after complete resection and represents a pre-invasive lesion. MIA shows ≤5 mm invasive focus; lepidic predominant adenocarcinoma has >5 mm invasive component with lepidic being the dominant histological pattern.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.