Background: Conventional cancer treatments face the challenge of therapeutic resistance, which causes poor treatment outcomes. The use of combination therapies can improve treatment results in patients and is one of the solutions to overcome this challenge. Chemotherapy is one of the conventional treatments that, due to the non‐targeted and lack of specificity in targeting cancer cells, can cause serious complications in the short and long‐term for patients by damaging healthy cells. Also, the employment of a wide range of strategies for chemotherapy resistance by cancer cells, metastasis, and cancer recurrence create serious problems to achieve the desired results of chemotherapy. Accordingly, targeted therapies can be used as a combination treatment with chemotherapy to both cause less damage to healthy cells, which as a result, they reduce the side effects of chemotherapy, and by targeting the factors that cause therapeutic challenges, can improve the results of chemotherapy in patients.Recent Findings: Small molecules are one of the main targeted therapies that can be used for diverse targets in cancer treatment due to their penetration ability and characteristics. However, small molecules in cancer treatment are facing obstacles that a better understanding of cancer biology, as well as the mechanisms and factors involved in chemotherapy resistance, can lead to the improvement of this type of major targeted therapy.Conclusion: In this review article, at first, the challenges that lead to not achieving the desired results in chemotherapy and how cancer cells can be resistant to chemotherapy are examined, and at the end, research areas are suggested that more focusing on them, can lead to the improvement of the results of using targeted small molecules as an adjunctive treatment for chemotherapy in the conditions of chemotherapy resistance and metastasis of cancer cells.

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.

Conventional cancer treatments face the challenge of therapeutic resistance, which causes poor treatment outcomes. The use of combination therapies can improve treatment results in patients and is one of the solutions to overcome this challenge. Chemotherapy is one of the conventional treatments that, due to the non-targeted and lack of specificity in targeting cancer cells, can cause serious complications in the short and long-term for patients by damaging healthy cells. Also, the employment of a wide range of strategies for chemotherapy resistance by cancer cells, metastasis, and cancer recurrence create serious problems to achieve the desired results of chemotherapy. Accordingly, targeted therapies can be used as a combination treatment with chemotherapy to both cause less damage to healthy cells, which as a result, they reduce the side effects of chemotherapy, and by targeting the factors that cause therapeutic challenges, can improve the results of chemotherapy in patients. Small molecules are one of the main targeted therapies that can be used for diverse targets in cancer treatment due to their penetration ability and characteristics. However, small molecules in cancer treatment are facing obstacles that a better understanding of cancer biology, as well as the mechanisms and factors involved in chemotherapy resistance, can lead to the improvement of this type of major targeted therapy. In this review article, at first, the challenges that lead to not achieving the desired results in chemotherapy and how cancer cells can be resistant to chemotherapy are examined, and at the end, research areas are suggested that more focusing on them, can lead to the improvement of the results of using targeted small molecules as an adjunctive treatment for chemotherapy in the conditions of chemotherapy resistance and metastasis of cancer cells.