Cancer chemotherapy, also known as Immuno-oncology, involves activating the immune system to treat cancer and enhance its innate ability to defeat the cancer. It is a practical application of basic research in cancer immunology and a developing field of oncology. Cancer immunotherapy is based on the fact that cancer cells frequently include tumour antigens, chemicals that can be recognised by immune system antibody proteins and bind to them. Frequently, proteins or other macromolecules function as the tumour antigens (eg: carbohydrates). Normal antibodies bind to external pathogens, while modified immunotherapy antibodies bind to tumour antigens, locating and identifying cancer cells for the immune system to inhibit or destroy. Cancer's development in the clinic, because efficacy of immunotherapy varies greatly across various cancer types; for instance, several subtypes of gastric cancer respond well to the treatment, whereas other subtypes need not respond favourably. Both active and passive immunotherapies occur. Through the immune system, active immunotherapy selectively targets tumour cells.

In contrast, passive immunotherapy improves the immune system's capacity to fight cancer cells rather than directly targeting tumour cells. Checkpoint inhibitors and cytokines are two examples. Active cellular therapies attempt to destroy cancer cells by identifying certain antigens, often known as biomarkers, in the patient's body. The purpose of cancer vaccines is to use a vaccine to trigger an immune response to these antigens. There is only one vaccination available right now, called sipuleucel-T for prostate cancer. Immune cells are extracted from the patient, genetically modified to recognise tumor-specific antigens, and then restored to the patient via cell-mediated therapies like CAR-T cell therapy. Natural killer (NK) cells, lymphokine-activated killer cells, cytotoxic T cells, and dendritic cells are instances of cell types that can be employed in this manner. Finally, it is possible to produce specific antibodies that can identify cancer cells and instruct the immune system to target them. Examples of such antibodies include rituximab (targeting CD-20), trastuzumab (targeting HER-2), and cetuximab (targeting EGFR).  The objective of passive antibody treatments is to increase immune system activity without specifically targeting cancer cells. For particular, cytokines directly activate and stimulate the immune system. Immunological checkpoint proteins that normally suppress the immune response are the targets of checkpoint inhibitors. This enhances the immune system's capacity to combat cancer cells. New potential targets for enhancing immune function are being discovered by current research. Checkpoint inhibitors with FDA approval include the antibodies ipilimumab, nivolumab, and pembrolizumab.