To dissect the mechanism of how ERα in the lung cancer cells increases the infiltrating M2 macrophages with higher MMP9 production, we then examined those cytokines that have been linked to the macrophage recruitment and polarization (Ao et al., 2017; Izumi et al., 2013; Lee et al., 2013; Murdoch et al., 2004; Nagarsheth et al., 2017; Sánchez‐Martín et al., 2011; Su et al., 2014; Wang et al., 2013; Yeh et al., 2016). Here, MMP9 is linked to lung cancer.