Spread through air spaces is a common phenomenon of pulmonary metastasized tumours regardless of origins

OBJECTIVES: Spread through air spaces (STAS) is a unique pattern of invasion in primary lung cancers. However, little is known about STAS in pulmonary metastases (PMs). This study was to investigate the incidence of STAS among PMs and the association between STAS and clinicopathological characteristics of PMs. METHODS: A total of 127 patients who underwent metastasectomy at our institution from June 2009 to December 2019 were retrospectively analysed. Survival analysis was performed in 40 patients with PM from colorectal cancer (CRC). RESULTS: STAS was identified in 33.1% of patients (42 of 127) with PMs. STAS was found in PMs of various primary cancers, including CRC, breast cancer, renal cell carcinoma, cholangiocarcinoma and osteogenic and soft tissue sarcoma, but the incidence varies. PMs originating from epithelial tissue showed higher incidence of STAS than those from mesenchymal tissue (45% vs 11%, P < 0.001). Elder age (P = 0.006) and primary sites (P < 0.001) were significantly correlated with STAS. In patients with PMs from CRC, the presence of STAS was an independent predictor of shorter recurrence-free survival (hazard ratio = 10.25, P= 0.002) and poor overall survival (hazard ratio = 4.75, P = 0.047) by multivariable analysis. CONCLUSIONS: STAS might be a lung-specific tumour invasion pattern and STAS is commonly observed in PMs of different origins. The incidence of STAS was significantly higher in PMs originating from epithelial tissues than those from mesenchymal tissues. Presence of STAS was an independent predictor of poor prognosis in patients with PM from CRC.