EP1.18-09 Analysis of the Role of Postoperative Radiotherapy in Pathological N2 Non-Small Cell Lung Cancer with Propensity Score Matching

Abstract

N2 non-small cell lung cancer (NSCLC) is a heterogeneous disease. For operable patients with postoperative N2 non-small cell lung cancer, the optimum adjuvant treatment strategy is still in dispute. Our aim was to assess the efficacy of conbine postoperative chemoradiotherapy (POCRT) or postoperative chemotherapy (PCT) alone following surgery in pathological N2 non-small cell lung cancer using propensity score matching, and to explore the factors influencing the prognosis. Between 2004 and 2014, a total of 175 patients fulfilled the inclusion criteria. The initiation of PCT started later than 2 weeks after the operation. The regimens of PCT in the present study included a cisplatin-based regimen and were administered for at least 2 cycles. POCRT was executed sequentially or sandwiched with PCT with three-dimensional conformal radiotherapy(3D-CRT) or intensity-modulated radiotherapy technique(IMRT). The prescription dose to clinical target volume (CTV) was 50 (range 44-60) Gy, Data were analyzed using SPSS version 24.0. Survival curves were produced using the Kaplan-Meier estimator method and compared with the log-rank test. Univariable and multivariable analyses of clinical characteristics. All available patient and tumor variables were compared using the χ2 test. Propensity score matching (PSM) analyses were used to compensate for differences in baseline characteristics between the POCRT and PCT groups to confirm the survival difference. The survival of the two groups was followed up and the effect of postoperative radiotherapy was analyzed. The median survival time was 57 vs 40 months in the POCRT and PCT groups, and the 1, 3 and 5-year OS rates in the POCRT and pCT groups were 98.3 vs. 86.1%, 71.7 vs.53.0% and 45.7 vs. 39.0%, respectively (P=0.019). Exploratory subgroup analysis found that compared with PCT, POCRT improved OS in patients with squamous cell subtype (P=0.010), no lymphovascular invasion (P=0.006), pN2a (P=0.006) or total number of metastatic lymph nodes ≤7 (P=0.016). Following PSM, a total of 113 events were identified in both the POCRT and PCT groups, with 60 and 53 patients in each group, respectively. There was no significant difference in the general clinical data between the two groups after matching. The median survival time was 57 vs 63 months in the POCRT and PCT groups after matching, and the 1, 3 and 5-year OS rates in the POCRT and PCT groups were 98.3 vs. 92.5%, 71.7 vs. 64.2% 和 45.7 vs. 50.7% respectively, with no significant difference (P=0.463). Following PSM, the survival differences between POCRT and PCT in the various subgroups were not statistically significant, except in patients with squamous cell lung cancer (P=0.010), there was also a trend toward an increase in the overall survival of pN2-NSCLC with pN2a (P = 0.196) or total number of metastatic lymph nodes ≤7 (P=0.367). Univariate and multivariate analyses indicated that T stage, total number of MLNs and POCRT were independent factors affecting OS. POCRT following complete resection clearly demonstrated superior survival compared with pCT. And POCRT may be specifically recommended to N2 patients with squamous cell lung cancer, particularly those with limited nodal involvement and T4 disease.