FOLR2 and neoplasm: In line with these data and the observation that soluble factors released by cancer cells mediate the upregulation of FRβ expression by human macrophages25, macrophages obtained from tumor-free mice, which expressed low levels of FRβ, significantly upregulated FRβ when cultured in the presence of ID8 tumor cell supernatants for 24 h (Fig. 1c).