Cancer is a complex and dynamic disease that can rapidly spread throughout the body and weaken the immune system. Although immune cells play a significant role in combating cancer cells, the immune response alone is often insufficient to completely eliminate the tumor. Therefore, selecting an appropriate treatment strategy according to the patient’s condition is essential. In this study, the effects of chemotherapy and immunotherapy, both individually and in combination, on the populations of cancer cells and immune cells were investigated. The proposed model considers cellular interactions, drug resistance in cancer cells, and the role of macrophages in the immune response. Simulations were performed using Simulink in the MATLAB environment. The results indicate that in patients with a small initial tumor size and a strong immune system, the immune system alone can eliminate cancer cells without therapeutic intervention. However, in patients with a large initial tumor size, the combination of immunotherapy and chemotherapy is the most effective treatment strategy, leading to complete eradication of cancer cells within 9 days while preserving the patient’s overall health.