CSF1R and neoplasm: The relative absence of detectable ECFP in most tissue macrophages of the MacBlue mouse, and also in the tumour-associated macrophages, where it is present on blood monocytes (including those within the tissues) could mean either that (a) the ECFP is rapidly extinguished as cells differentiate to become tissue macrophages or (b) the monocytic precursors of tissue macrophages are actually the F4/80+, CSF1R+ immature myeloid cells which lack ECFP (and which are also the precursors of mature monocytes) or (c) the tissue macrophages are maintained entirely by self-renewal.