Clinicopathological characteristics of lung adenocarcinoma with compound EGFR mutations

The extensive clinical applications of next-generation sequence analyzers have made uncommon and compound EGFR mutations more prevalent than previously described. However, clinicopathological impacts of compound EGFR mutations in lung adenocarcinoma remain unclear. We earlier examined the presence of compound EGFR mutations primarily in the cis allele by EGFR exon sequencing and droplet digital polymerase chain reaction in 462 completely resected EGFR-mutated adenocarcinomas of the lung and identified 64 tumors with compound mutations. We evaluated clinicopathological characteristics of lung adenocarcinomas with compound EGFR mutations in comparison with cases with common or uncommon single mutations. Among 64 compound EGFR mutations, L858R/E709G (9%) was the most frequent mutation type, followed by L858R/S768I (8%), L858R/T790M (8%), and L858R/L833V (6%). We observed both single and compound mutations frequently in women, never or light smokers; their adenocarcinomas showed thyroid transcription factor-1 immunoreactivity. In contrast, compound mutations were significantly associated with lymph node metastases (p = 0.0242; single vs. compound cases) and the presence of tumor cells with clear cytoplasm (p = 0.0014; single vs. compound cases). Furthermore, patients with compound mutations had significantly poorer prognoses than cases with single EGFR mutations (p = 0.043). Overall, clinicopathological features of common, uncommon, and compound EGFR mutations are similar; however, tumors with compound mutations may be characterized by aggressive behavior and histological findings of clear cell features.