Histopathological and molecular profiling of lung adenocarcinoma skin metastases reveals specific features

Aims Little is known regarding the histopathological and molecular features of lung adenocarcinoma skin metastases. Our study is the largest, to our knowledge, to comprehensively explore these to date. Methods and results We performed a retrospective cohort study analysing 42 lung adenocarcinoma skin metastasis samples obtained from a database of 2659 lung adenocarcinomas collected between 2010 and 2020. EGFR exon 19 deletion was detected in one patient and KRAS mutations were detected in 12 (33.3%) patients. The programmed cell death ligand 1 (PD‐L1) tumour proportion score was <1% in 27 patients, ≥1% and <50% in eight patients, ≥50% in six patients and not assessable in one patient. We showed that the predominant histopathological subtype is different from that at other metastatic sites ( P = 0.024). Thyroid transcription factor I (TTF‐1) was more often negative in skin metastases compared to other sites ( P < 0.001). The EGFR mutation rate tended to be lower for skin metastases compared to other sites ( P = 0.079). Skin metastases were associated with a high rate of PD‐L1‐negative cases ( P = 0.022). Conclusion Our work shows that the skin metastases of lung adenocarcinoma have a specific histopathological profile.