SIGLEC12 and neoplasm: Earlier we emphasised that SIGLEC12 is expressed by macrophages, Markiewski et al. (2009) suggested that IgM and IgG, by-products of plasma cells, can bind with tumour antigens to form an antigen-antibody complex, this further results in Fc gamma receptor activation and opsonization with complement 1 (C1), thereby activating the complement system cascade [48].