Biological Difference between L858R and Exon 19 Deletion Contributes to Recurrence-Free Survival of Resected Non-Small Cell Lung Cancer

Introduction: The differences in biological characteristics among different genotypes of classical EGFR mutations have not been clarified. This study aimed to clarify the clinical and biological differences between L858R and 19 deletion in NSCLC. Methods: We analyzed a cohort of 191 consecutive cases of surgically resected NSCLC harboring EGFR driver mutations (L858R or 19 deletion) in which curative resection was performed in Aichi Cancer Center Hospital, Nagoya, Japan, from January 2006 to September 2021 and in which recurrence subsequently developed. We also subjected 61 surgically resected NSCLC specimens harboring EGFR driver mutations (L858R or 19 deletion) to an RNA sequencing analysis. Results: In patients with stage I disease, the median time to recurrence did not differ to a statistically significant extent between the types of EGFR mutations; however, among those with stage II and III disease, the median time to recurrence in patients with the L858R genotype tended to be shorter in comparison to those with 19 deletion (log-rank test, p = 0.47 and 0.46, respectively). In comparison to 19 deletion tumors, L858R tumors had higher cytological malignancy (e.g., mitotic ability) and showed stronger immunogenicity. Conclusion: L858R and 19 deletion tumors are likely to have a slight difference in the time to recurrence. They suggest that even in EGFR driver tumors, which are treated as the same disease category, the biological characteristics of the tumors are different, which may leave room for innovations in postoperative treatment and treatment at recurrence.