MRC1 and neoplasm: 21 Monteiro et al showed that almost all infiltrating macrophages in malignant canine mammary tumors were CD206-positive, further supporting the notion that TAMs are M2-skewed in dogs and have a central role in the tumor microenvironment.38 The scavenger receptor CD204 has been shown to be a good marker for canine macrophages, with no cross-reactivity with dendritic cells under normal conditions or undifferentiated blood monocytes.27,56