The following section is on a treatment of cancer, it is not a guide on how to perform it, nor is it a guide as to the side effects or how to prepare for treatment. The following section is designed to give readers an in-depth understanding of the treatment, how it functions, and why it functions. Please note that researchers are constantly working to find new treatments or improve current ones, this means the subject(s) discussed below are likely to change as medicine improves.
Chemotherapy is the most well known but arguably least understood treatment of cancer. The term chemotherapy refers to the use of drugs to treat cancer, chemotherapy does not refer to a specific drug but rather a category of drugs that can be used for this purpose. There are over 100 different drugs(1) that can be used as chemotherapeutics and this page will not go into all of them but will cover how they work more broadly.
Note: other sections in this paper such as targeted therapy and immune therapy can be considered chemotherapies as well but are a subset of chemotherapies that work in very different ways and will thus be explored separately. Even some types of hormone therapy can be considered targeted therapies which can in turn be considered chemotherapies making the whole categorisation unnecessarily complex especially when exploring different sources that may categorise these differently.
Generally speaking most common chemotherapies work as a poison, these chemotherapeutics can be referred to as cytotoxic and this is the only type covered in this section as other types of chemotherapeutics fall into other categories mentioned above. The idea of cytotoxic chemotherapies is to exploit the slight differences between cancerous and healthy cells, generally cancerous cells replicate faster than most healthy cells and that is the difference most of these drugs harness. A lot of cytotoxic chemotherapies therefore work by disrupting something in the process of mitosis or DNA replication (S phase) as healthy cells should be performing these processes far less than cancerous cells. For example anti microtubular drugs disrupt the mitotic spindles that attach to chromosomes and pull them apart during mitosis, by freezing the cell in this vulnerable state it usually dies. (2)
Chemotherapies have significant advantages in cancer treatment. Chemotherapies can be introduced systemically usually intravenously meaning the drug can travel all around the body attacking all the present tumors at once, even tumors that have yet to cause symptoms or be noticed at all can die to this treatment. This makes it an attractive choice for late stages of cancer where tumors have spread to multiple areas. It can also be used to follow up other treatments in order to ensure any remaining cancerous cells that may have been missed or are already forming smaller tumors elsewhere are also killed.
Chemotherapy does not come without challenges however, by targeting the fast growing nature of cancerous cells other fast growing cells such as hair follicles, gut epithelial cells, and bone marrow can also be affected. Generally these healthy cells will have more functional repair systems than the already damaged mutated and dysfunctional cancer cells meaning they will be damaged less than the cancer cells and are capable of recovering, however symptoms such as baldness, ulcers, and low blood cell counts are common.
Tumors can also become resistant to chemotherapies, the fast replication and lack of checkpoints in cancerous cells often leads to abnormally fast mutation. With increased mutations comes increased genetic variability, this means there is increased chance of a cell mutating in a way that makes it resistant or immune to the treatment, for example the cell could expel the drug or circumvent the process it targets. If that were to happen that specific mutation would then survive longer thus replicating more than the other cells, eventually these cells can be the only ones left meaning the entire tumor is now immune or resistant to that chemotherapeutic. This process is very similar to the process of evolution, specifically asexual evolution.
Some tissues can also naturally take up less of certain drugs, for example cancers in the pancreas often get less blood flow than other cancers and can form layers of tissue around it that do reduce the speed it develops but also makes it exceptionally hard to treat. Cancers in the brain can also be harder to treat with chemotherapies as the blood brain barrier can often block certain treatments.
| 1. | Gersten T. Types of chemotherapy: MedlinePlus Medical Encyclopedia. Medlineplus.gov. Published 2016. Accessed July 17, 2026. https://medlineplus.gov/ency/patientinstructions/000910.htm |
| 2. | Chan KS, Koh CG, Li HY. Mitosis-targeted anti-cancer therapies: where they stand. Cell Death & Disease. 2012;3(10):e411-e411. doi:10.1038/cddis.2012.148 |