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Background: Thymosin β10 (TMSB10) has been reported to play a protumorigenic role in a majority of solid cancers. However, the existence of TMSB10 in immune microenvironment may contribute to the pathogenesis of lung adenocarcinoma has not been previously explored.Method: TAMs-associated TMSB10 expression was evaluated by immunohistochemistry (IHC) in 184 lung adenocarcinomas. Xenograft mice model was established to investigate the effect of TMSB10 shRNA on TAMs phenotypes. The macrophages phenotype associated cytokines IL-6, IL-8, IL-12 and TNF-α were detected by ELISA after treated with TMSB10 shRNA or scramble. Furthermore, the target proteins were detected by immunoblotting.Results: We found that high TAMs-associated TMSB10 expression was significantly correlated with the advanced TNM stage and T3/T4 tumor size. And high TAMs-associated TMSB10 expression was significantly correlated with poor overall and progression-free survival of lung adenocarcinoma, acting as an independent prognostic factor for lung adenocarcinoma. Furthermore, we investigated the biological functions of TMSB10 in macrophages in vivo and in vitro. TMSB10 knockdown dramatically reduced TAMs, THP-1 and RAW264.7 cell proliferation, and promoted macrophages phenotype conversion of M2 to M1, and TMSB10 knockdown reduced the levels of p-Akt (Sec473), p-mTOR (Sec2448) and p-p70S6K (Thr389) without effect on Akt, mTOR and p70S6K expression.Conclusions: These results demonstrate that TAMs-associated TMSB10 promotes tumor growth through increasing TAMs M2 conversion and proliferation via PI3K/Akt signaling pathway, providing a promising tumor biomarker for predicting prognosis and a potential therapeutic target for lung adenocarcinoma. [ABSTRACT FROM AUTHOR]