FP08.04 Tumour Spread Through Air Space (STAS) In Lung Metastases

To evaluate the presence of tumour spread through air space (STAS) in lung metastases and its possible impact on prognosis. This is a retrospective study of prospectively collected data of patients (pts.) who underwent lung metastasectomy (January 2004 - December 2018) in our Thoracic Surgery division. Tissue slides were retrieved from the Pathology division for STAS evaluation of the metastatic nodule tissue. STAS was defined according to the 2015 WHO definition for lung tumors. Exclusion criteria for STAS included: cell clusters very proximal to the tumour margin; presence of neoplastic cells into the blood/lymphatic bronchial vessels; tumoural cell clusters present in incomplete or split areas of the section; presence of cell clusters distant from the tumour margin due to possible mechanical transposition. A blinded revision of all the archived tissue slides was individually performed by two trained pathologists with the aim of evaluating the presence of STAS. Discordant cases were jointly revised and discussed to reach a univocal opinion on each case. Differences between continuous and discrete variables were evaluated by t-student and Fisher’s exact test or chi-square test. Overall survival (OS) was analysed using Kaplan-Meier method, log rank test, and Cox proportional hazards model. Presence of STAS was put in relation to clinical and pathological characteristics; follow-up; histology; MTS dimension; MTS site; number of subsequent metastasectomies; TNM score of the primary tumour; OS; disease free survival (DFS); time to progression (TTP) . Three-hundred metastasectomies were retrieved of which 184 samples were considered for the study (81 pts. were excluded because lost at follow-up, 35 samples were not analysable). One-hundred and seven pts. were males (58%), 95 were smokers (56,5%), median age was 61yrs (range:16-82). STAS was found in all histotypes but was significantly prevalent in the adenocarcinoma histology (p<0.001). Overall, the presence of STAS seemed not to impact DFS however, in the adenocarcinoma subset, STAS was related to a worse DFS (p<0.04) and TTP (p<0.05) and STAS+ colorectal adenocarcinoma metastases were correlated to a worse TTP if compared to other STAS+ histotypes (p<0.029) (Fig.1). STAS was present in lung metastases but significantly more present in the adenocarcinoma subgroup with a more aggressive behaviour, especially the colorectal one. Further studies are needed to confirm our preliminary results.