A 62-year-old non-smoker woman presents with a peripheral lung adenocarcinoma showing lepidic growth pattern — tumor cells growing along intact alveolar walls without stromal invasion. What is this histological subtype and its significance?
- A Adenocarcinoma in situ (AIS) — formerly bronchioloalveolar carcinoma (BAC); excellent prognosis with near 100% 5-year survival after complete resection ✓
- B Acinar adenocarcinoma; intermediate prognosis with mixed gland formation
- C Mucinous adenocarcinoma; high mucin production correlating with worse prognosis
- D Solid adenocarcinoma; worst prognosis among adenocarcinoma subtypes
Correct answer: A. Adenocarcinoma in situ (AIS) — formerly bronchioloalveolar carcinoma (BAC); excellent prognosis with near 100% 5-year survival after complete resection
Explanation
Pure lepidic growth pattern without invasion, measuring ≤3 cm, defines adenocarcinoma in situ (AIS), formerly called bronchioloalveolar carcinoma (BAC). AIS carries an excellent prognosis with near 100% 5-year disease-specific survival after complete surgical resection because it lacks invasive components. Once any invasion is present (even <5 mm), it is reclassified as minimally invasive adenocarcinoma or invasive adenocarcinoma (predominant lepidic pattern). EGFR mutations are common in this subtype.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.