Breast cancer (BC) stands as the most prevalent malignant tumor among females. Tailored treatments may involve monoclonal antibody therapy and hormone therapy, potentially improving prognosis. Tumor stroma cells are known to significantly influence tumor behavior and response to treatments. For instance, macrophages (MΦs) are highly plastic innate immune cells commonly abundant in tumors that can transition between pro-inflammatory (M1) and anti-inflammatory (M2) phenotypes in response to environmental cues. Tumor-associated MΦs (TAMs) often display characteristics similar to M2 cells, thereby promoting tumor growth and invasiveness. Within the breast tumor microenvironment, TAMs have emerged as the predominant immune cell components, exerting pivotal influence over BC tumorigenesis and progression. Therefore, their involvement in BC development has recently established TAMs as novel and promising targets for BC treatment. ADP-ribosylation is a posttranslational modification mediated by a family of poly(ADP-ribose) polymerase (PARP) enzymes, known to regulate various cellular functions e.g. DNA repair, gene transcription and cell death in different cell types, including MΦs. Specifically, PARP14 is gaining attention as a potential target for chronic inflammation and has been implicated in tumor promotion. However, its precise roles in tumor immune evasion and involvement in TAM polarization still lacks comprehensive understanding and remains poorly understood. In the first study, we investigated the role of PARP enzymes in this process. We found that the PARP inhibitor (PARPi) PJ34 and the specific PARP14 inhibitor MCD113 reduced the expression of M2 marker genes in primary murine, in THP-1 monocytic human and in primary human monocyte-derived MΦs polarized with IL-4. Mice lacking PARP14 showed reduced ability to differentiate into M2 cells. In mouse and human models of TAMs, both PARPis and PARP14 knockout (KO) weakened TAM polarization, leading to increased cancer cell apoptosis. Moreover, lipocalin-2 (LCN2), macrophage migration inhibitory factor (MIF) and plasminogen activator inhibitor-1 (PAI-1) were identified by protein profiling arrays as potential (ADP-ribosyl)ation-dependent mediators of TAM differentiation. Our results suggest that inhibiting PARP14 could be a promising strategy for cancer treatment by reprogramming TAM behavior to enhance anti-cancer immune responses. Monoclonal antibody immunotherapy is a key part of BC treatment, with antibody-dependent cellular cytotoxicity (ADCC) being one of its mechanisms. In this scenario, the antibody binds to cell surface antigens on the cancer cells and engages Fc receptors on immune cells, e.g. natural killer (NK) cells, activating cytotoxic immune responses, to eliminate the tumor. Enhancing the effectiveness of these therapies requires novel chemicals that boost cancer cell sensitivity or immune cell potency. Based on our recent findings, in the second project we developed a cancer ADCC spheroid model and outline a protocol to find ADCC-modulating drugs. Three-dimensional (3D) models e.g. cancer spheroids are superior to 2D cultures in predicting in vivo responses of tumors to anticancer therapies. By utilizing 3D models, we established co-cultures of human epidermal growth factor receptor 2-positive (HER2+) BC cells and NK cells, inducing ADCC with Trastuzumab. Using a sensitive probe to measure apoptotic cell death and image analysis with an automated microscope, we distinguished live and dead killer and target cells. With our method, compatible with high-throughput screening, we demonstrated that Sunitinib, a Food and Drug Administration (FDA)-approved cancer drug, significantly reduces ADCC. This approach offers a platform for screening ADCC-modulating compounds in cancer cell spheroids, and, importantly, it can be applied to several assays of interest.