Primary collision lung adenocarcinoma harboring EGFR exon 21 L858R and KRAS G12C mutations: A case report

Pulmonary collision tumors are characterized by the coexistence of two morphologically and genetically distinct neoplasms within a single lesion. We report a rare case of primary collision lung adenocarcinoma harboring two mutually exclusive driver mutations, EGFR exon 21 L858R and KRAS G12C. A 77-year-old man with a history of smoking was diagnosed with lung adenocarcinoma. Preoperative molecular testing of a transbronchial biopsy specimen suggested the coexistence of EGFR L858R and KRAS G12C mutations. Pathological findings of the surgically resected tumor exhibited solid and papillary architecture, with a lepidic pattern at the periphery. DNA was extracted separately from the solid/papillary and lepidic components for molecular analysis. The solid/papillary component harbored a KRAS G12C mutation but lacked an EGFR mutation, with a PD-L1 tumor proportion score (TPS) of 5%. In contrast, the lepidic component harbored an EGFR L858R mutation without a KRAS mutation and had a PD-L1 TPS of