Similar to human breast cancers known to be highly infiltrated by macrophages (Biswas et al., 2016; Dent et al., 2007; Perou et al., 2000; Garrido-Castro et al., 2019; Khan et al., 2019; Marra et al., 2019; DeNardo and Ruffell, 2019; Lim et al., 2018; Wagner et al., 2019; Biswas and Mantovani, 2010; Tan et al., 2019; Adams et al., 1987; Hajitou et al., 1998; Giordano et al., 2001), the macrophage population (CD11b+F4/80+) constituted a large portion of the non-malignant cellular component of EF43.fgf4-derived mammary tumors, followed by a lesser population of B lymphocytes (CD45R+). The gene discussed is FGF4; the disease is breast carcinoma.