110P The role of extensive lymph node dissection in the new grading system for lung adenocarcinoma

This study evaluates the prognostic impact of the newly established grading system for lung adenocarcinoma, with stratification based on the extent of lymphadenectomy. The study population comprised 1,258 patients with lung adenocarcinoma who underwent curative resection between 2006 and 2017. It focused on correlating overall survival (OS) and recurrence-free survival (RFS) with tumor grades. Lymphadenectomy was categorized into two groups based on completeness: IASLC-R0 and R(un). The cohort's median age was 62 years and included 41.9% males. The majority (80.9%) underwent lobectomy or more extensive procedures. The tumor distribution was 274 grade 1, 558 grade 2, and 426 grade 3 cases. The median follow-up period was 102.0 months. The 10-year OS/RFS rates differed significantly across grades 1-3: 92.4%/99.2%, 77.8%/81.3%, and 63.6%/59.1%, respectively (p < 0.001). Multivariate Cox regression analysis identified lymph node resection status R(un) (HR = 1.70, p = 0.001) and histological grade 3 (HR = 1.57, p = 0.010) as independent prognostic factors for RFS. Furthermore, the extent of lymphadenectomy, IASLC-R0 versus R(un), revealed significant survival differences in grade 3 tumors, but not in grades 1 and 2. Patients with grade 3 tumors who underwent IASLC-R0 lymphadenectomy showed notably better OS and RFS (p < 0.001), a finding that was maintained even after propensity score matching (p = 0.007 for OS, 0.006 for RFS). Additionally, significant differences in recurrence patterns between IASLC-R0 and R(un) groups were observed in patients with grade 3 tumors (p=0.002). The incidence rates for local, distant, and simultaneous local and distant recurrences were 8.5% versus 13.7%, 11.0% versus 12.2%, and 11.0% versus 20.6%, respectively. The new grading system demonstrates a decrease in surgical outcomes for lung adenocarcinoma across grades 1-3. IASLC-R(un) does not improve OS or RFS in grades 1 and 2 but significantly worsens OS and RFS in grade 3. Therefore, for patients with grade 3 lung adenocarcinoma, adjuvant therapy and intensive monitoring are recommended for improved outcomes.