Metastasis of lung adenocarcinoma to the colon is a rare condition. Here, we present a case of a male patient with colonic metastatic lung adenocarcinoma. Following the diagnosis of metastatic lung adenocarcinoma with pleural and pericardial involvement and subsequent immunotherapy, our patient was found to have a descending colon polyp. Histological examination showed a tubular adenoma, yet sheets of pleomorphic epithelioid malignant cells were seen infiltrating from the base of the polyp into the lamina propria, suggesting a metastatic nature of the malignant cells. Immunohistochemical analysis revealed patchy positive staining for MNF116 and Cam5.2 and negativity for CK5/6, CK7, CK20, TTF1, melanocytic, and lymphoid markers. Further confirmation came from molecular profiling of the colonic metastatic cells, which revealed KRAS (Exon 2, c.34G>T) and TP53 (Exon 8, c.796G>T) mutations consistent with the primary lung adenocarcinoma. The patient subsequently underwent restaging imaging and chemotherapy. This case illustrates the unusual histological morphology of colonic metastatic lung adenocarcinoma following immunotherapy and highlights the diagnostic difficulties of this condition, emphasizing the critical role of multi-modal studies, including immunohistochemical and molecular analyses.
Luo et al. (2026) studied this question.