ACTA1 and neoplasm: Ki67+ proliferating cells were visualized predominantly in Erbb2+ tumors, and anti-PD-1 mAb treatment did not alter the percentages of Erbb2+, Ki67+, CD11b+ monocytic myeloid cells, CD31+ endothelial cells or αSMA+ fibroblasts/pericytes; however, a significant increase in tumor-associated F4/80+ macrophages (p < 0.025) was observed (Figure 2E).