Intensity of SLX predicts distance of tumor spread through alveolar spaces in stage I lung adenocarcinoma

BACKGROUND: Tumor spread through alveolar spaces (STAS) is a recently described invasive pattern associated with the prognosis and recurrence of lung adenocarcinoma. This study was performed to determine whether the presence and distance of STAS can be predicted by the immunohistochemical intensity of SLX, a well‐known cell adhesion protein. METHODS: In total, 245 patients with pathological stage I lung adenocarcinoma who underwent lobectomy with radical mediastinal lymph node dissection were identified from 1998 to 2012. Recurrence‐free survival (RFS) was compared between patients stratified by STAS and the immunohistochemical intensity of SLX in the main tumor. Patients were divided into three groups based on the intensity of SLX staining: high (n = 108), moderate (n = 48), and low (n = 89). RESULTS: STAS was observed in 71 patients (29.0%). Patients with STAS had significantly poorer five‐year RFS (67.1%) than those without STAS (84.8%). Although no relationship was observed between the existence of STAS and SLX intensity, the distance between STAS cells and the main tumor was significantly shorter in the moderate group (median 0.9 mm, range: 0.2–1.2 mm) than in the other two groups (median 1.2 mm, range: 0.4–5.0 mm). The five‐year RFS rates in the high, moderate, and low groups were 80.0%, 96.0%, and 75.8%, respectively. Multivariate analysis revealed that pathological stage, lymphatic/vascular invasion, and SLX intensity were independent predictors of recurrence. CONCLUSION: SLX staining cannot predict the presence of STAS; however, it can predict the distance between STAS and the main tumor in stage I lung adenocarcinoma.