Extra-capsular growth of lymph node metastasis correlates with poor prognosis and high SOX9 expression in gastric cancer

Abstract

Background: Extra-capsular growth (ECG) describes the extension of neoplastic cells beyond the lymph node capsule. Aim of this study was to investigate the prognostic value of ECG and its association with a stem cell like phenotype indicated by expression of the transcription factor SOX9 in gastric cancer.

Methods: By histological evaluation, 199 patients with nodal positive gastric cancer or adeoncarcinoma of the esophageal-gastric junction (AEG) were divided into two groups according to the presence (ECG) or absence (ICG) of extracapsular growth in at least one nodal metastasis. Of these, 194 patients were stained for SOX9 and SOX2 using immunohistochemistry. Seventeen nodal negative patients (pT3/4, pN0, pM0) served as controls.

Results: Seventy-three patients (36.7%) showed ECG. ECG was associated with lower overall survival (p < 0.0001), advanced pT- (p = 0.03) and pN- category (p < 0.0001) and lymphovascular invasion (p = 0.014). In multivariate analysis, ECG was found to be an independent prognostic factor (HR = 2.1; 95% CI 1.7-3.4; p = 0.001). SOX9 expression correlated significantly with ECG (96% SOX9 high in ECG patients vs. 79% SOX9 high in patients with ICG; p = 0.002). Controls showed significantly reduced SOX9 expression compared to nodal positive carcinomas (59% vs. 85% high SOX9 expression; p = 0.006). No significant correlation of ECG and SOX2 (59% SOX2 negative in ECG patients vs. 64% in patients with ICG, p = 0.48) could be obtained.

Conclusions: Patients with ECG exhibit poorer prognosis and ECG was found to be an independent prognostic factor. Thus, ECG turns out to be a morphological biomarker for a more aggressive phenotype in gastric cancer. This is supported by the fact that ECG correlates with the expression of SOX9, which has been described in the context of pro-oncogenic properties of tumours. However, the fact that SOX2 failed to show significant results indicate that ECG is not associated with a distinct cancer stem cell phenotype in gastric cancer.

Keywords: ECG; Extranodal extension; Gastric cancer; Lymph node metastasis; Prognosis; SOX9.

Fig. 1

Flowchart showing the selection of nodal positive and nodal negative cases for histological evaluation of extra-capsular growth (ECG) and intra-capsular growth (ICG) as well as for immunohistochemical analysis of SOX9 expression

Fig. 2

Overview of lymph-node metastasis of gastric cancer with ECG (a) and ICG (b). The frames indicate areas shown with higher magnification in c and d (200 fold, hematoxylin and eosin stain), respectively

Fig. 3

Immunhistochemical staining of SOX9 and SOX2 in gastric adenocarcinoma (200-fold magnification). In a adenocarcinoma with high and in b with low immunohistochemical expression of SOX9 are shown. Adenocarcinoma with positive and negative SOX2 expression is shown in c and in d, respectively

Fig. 4

Proportion of cases with ECG and ICG (a) and its correlations with overall survival (b)

Fig. 5

Correlation of ECG with pT- (a) and pN-category (b), presence (pM1) or absence (pM0) of distant metastases (c) and with presence (L1) or absence (L0) of lymphangiosis carcinomatosa (d) according to TNM-classification of malignant s (8th edition 2017)

Fig. 6

Correlation of SOX9 and SOX2 expression with ECG and ICG (a, c) and with the presence or absence of lymph-node metastasis (b, d)