Cancer is a devastating disease, causing tremendous morbidity and mortality each year. Cancer can be considered as a genetic disease in the sense that instabilities in protooncogenes and tumor suppressor genes are among the hallmarks of cancer progression and metastasis. However, a particular cancer can express different proteins in different patients, making cancer a heterogeneous disease. This heterogeneity in part influences treatment resistance and failure. Therefore, it is crucial to understand the mechanism by which cancer cells develop and enhance resistance to different agents. This review aims to present the general paradigm and recent updates on cancer cell resistance to different antitumor agents. It demonstrates that tumor resistance results from a myriad of factors, including tumor microenvironment, supporting immune cells, and cancer stem cells. This interaction contributes to cancer cells overcoming the therapeutic effects of different classes of antitumor agents, such as cytotoxic chemotherapeutics, targeted agents, and immunotherapies. With the development of advanced molecular analysis, specialized genomic assessment has assisted clinicians and researchers in choosing selected agents combating cancer cells. Together, this approach can potentially reduce treatment toxicity, health system burden, and financial costs while improving patient quality of life. Understanding the exact mechanism of drug resistance in cancer cells can open the way to new effective and less toxic therapeutics.