This review delineates the complex roles of these cells within the neuropathological landscape, focusing on a range of signaling pathways—namely, NF-κB, microRNAs (miRNAs), and TREM2—that regulate the behavior of tumor-associated macrophages (TAMs) in GBM and disease-associated microglia (DAMs) in AD. The gene discussed is TREM2; the disease is neoplasm.