Analysis of clinical and pathological characteristics of 10 cases of fetal lung adenocarcinoma

Background Fetal adenocarcinoma of the lung (FLAC) is a rare subtype of lung adenocarcinoma resembling the developing fetal lung at the pseudoglandular stage (8–16 weeks of gestation). This study investigates the clinicopathological features, along with key diagnostic and treatment considerations for FLAC. Methods Clinical data from 10 FLAC patients diagnosed at Linyi People’s Hospital between January 2017 and December 2024 were retrospectively analyzed. Their clinicopathological characteristics were summarized in conjunction with relevant literature. Results The cohort comprised low-grade FLAC (L-FLAC, 6 cases) and high-grade FLAC (H-FLAC, 4 cases). Pathological examinations indicated higher frequencies of pleural invasion (3/4) and lymph node metastasis (1/4) in H-FLAC, which exhibited marked nuclear atypia and abundant mitoses, while L-FLAC demonstrated mild cellular atypia and morular structures. Immunohistochemistry revealed universal positivity for TTF-1. Napsin A expression was noted in both L-FLAC (3/3) and H-FLAC (2/4). In L-FLAC, β-catenin showed nuclear/cytoplasmic or nuclear expression in the vast majority of cases while H-FLAC displayed only membranous expression. Molecular testing detected an EGFR exon 19 deletion in one H-FLAC case and a KRAS G12C mutation in another. No recurrence was observed during follow-up, which ranged from 4 to 93 months. Conclusion FLAC exhibits distinctive morphological features and immunophenotypes, necessitating differential diagnosis from primary pulmonary tumors and metastatic malignancies. Surgical resection remains the primary therapeutic strategy. No disease recurrence was observed during follow-up from 4 to 93 months, although some patients had a shorter follow-up period of 4–6 months.