Differences between low and high grade fetal adenocarcinoma of the lung: a clinicopathological and molecular study

Fetal adenocarcinoma of the lung (FLAC) is a rare entity of lung cancer. It is classified into low-grade fetal adenocarcinoma (L-FLAC) and high-grade fetal adenocarcinoma (H-FLAC). We aim to report the clinicopathological and molecular features of FLAC in Chinese patients.

FLACs were screened from a consecutive lung adenocarcinoma series comprising 920 cases. The clinicopathological features L-FLAC and H-FLAC were retrospectively reviewed via immunohistochemical study and mutation analysis.

Three L-FLAC and five H-FLAC cases were identified. L-FLAC mainly occurred in young patients and was predominantly in stage I upon diagnosis and conferred favorable outcomes. L-FLAC tumors were characterized by the glycogen-rich columnar cells lining the complex glandular structures, with low nuclear atypia, morule formation, and mainly nuclear- and cytoplasmic-localized β-catenin expression. In contrast, H-FLAC predominantly occurred in elderly men with a history of smoking. The stage of H-FLAC was often advanced at presentation and had a poor prognosis. H-FLAC tumors exhibited more prominent atypia of the nucleus, the absence of morule formation, and largely membrane-localized β-catenin. All 5 H-FLACs were immunohistochemically characterized by overexpression of the p53 protein; the L-FLAC tumors were negative for p53. Two cases of H-FLAC were positive for AFP. No Her-2 or ALK-D5F3 overexpression was observed in any of the tumors. EGFR L858R point mutation was identified in one of the H-FLAC cases. EGFR T790M mutation was detected in one of the L-FLAC cases. No mutations in KRAS, PIK3CA or BRAF were detected.

L-FLAC and H-FLAC exhibited distinctive clinicopathological, immunophenotypic and molecular features with potential prognostic value.