This study examined the anti-cancer potential of the natural compound cardamonin in the tumor immune microenvironment (TIME) using genetically distinct triple-negative breast cancer (TNBC) cell lines: MDA-MB-231 (of Caucasian origin) and MDA-MB-468 (of African American origin). The investigation focused on PD-1/PD-L1 expression, an immune checkpoint targeted by current FDA-approved inhibitors to reverse the immunosuppressive effects of TIME; however, their success has been limited due to the gradual emergence of resistance to PD-1/PD-L1, emphasizing the need for new compounds that will be more effective in managing immunotherapy. The findings of this study show that TNBC cell treatment with cardamonin inhibited PD-L1 expression and downregulated PD-L1-precursor genes in both cell lines. In addition, cardamonin modulated the expression of antiinflammatory processes by decreasing the levels of CCL2 release, thereby reducing the chemoattraction of macrophages in the TIME, which may enhance the effectiveness of PD-1/PD-L1 inhibition and facilitate T-cell infiltration, thereby enhancing the host immune system. These findings suggest that cardamonin modulation of TIME holds promise in reversing resistance to PD-1/PD-L1 inhibition when used in conjunction with immunotherapy in TNBC treatment.