In the last edition, I spoke about what chemotherapy is and why it is given. This part is about the grouping of chemotherapies, how they work, and their side effects.
There are hundreds of different types of chemotherapy drugs. Chemotherapy can either work alone, as a single agent, or in combination with other types of anti-cancer therapies, such as immunotherapy or radiation therapy.
Because chemotherapies each differ in their chemical composition, they are divided into groups. These groups differ in the way cancer cells are destroyed and how effective they are for different cancer types.
Knowing and understanding these different groups helps doctors decide which chemotherapies to give for specific cancer types; how often to administer them; and in which combinations.
Also, because they work differently, each group can produce a different side effect profile. There are also certain side effects that are specific to individual chemotherapy drugs within a certain group.
Examples: cyclophosphamide, melphalan, and temozolomide (used for brain cancers).
How they work: prevent growth of cancer cells by damaging the DNA of the cancer cell.
What cancers they treat: breast cancer and lymphomas amongst many others.
Side effects: Alkylating agents work
on rapidly dividing cells, thus normal cells in the body that divide quickly in the body can also be affected. It can affect blood cells and bone marrow, causing anaemia (low haemoglobin) leading to fatigue; thrombocytopaenia (low platelets) which can cause bleeding; and neutropenia (low white blood cells) which can lead to infections.
Sometimes alkylating agents can cause secondary cancers many years after treatment but this is extremely rare (2% risk at 15 years).
Reproductive tissue is also affected with possible fertility issues. If you’re still planning to have children, it’s important to discuss fertility-sparing with your oncologist.
Many of these agents can also cause hair loss and problems with the gastrointestinal tract, such as diarrhoea or constipation. Nausea is also more common with this group, although nausea has a higher risk with some, such as cisplatin, and then also with certain combinations, such as cyclophosphamide with doxorubicin.
Platinum chemotherapy agents, such as cisplatin, carboplatin and oxaliplatin, also fall under alkylating agents. Platinum agents, especially cisplatin, have a higher risk of causing damage to the kidney, whereas oxaliplatin often causes neuropathies (pins and needles/numbness in the hands and feet).
Examples: 5 fluorouracil (5FU), cytarabine and gemcitabine.
How they work: interfere with both DNA and RNA by substituting its normal building blocks.
What cancers they treat: intestinal cancers, such as colon and stomach, and some leukaemias.
Side effects: These generally tend to cause mucositis (inflammation of the lining in the mouth) with or without mouth ulcers, and low blood counts. They rarely cause alopecia and usually result in minimal nausea.
This group is divided into anthracycline and non-anthracycline.
How they work: change the DNA within cancer cells so that they can’t grow and multiply.
Examples: doxorubicin (Adriamycin), daunorubicin and idarubucin. These are usually red in colour and have infamously been dubbed the ‘red devil’ by many patients.
How they work: interfere with specific enzymes that are involved in copying DNA during the cell cycle.
What cancers they treat: breast cancer, lymphoma, sarcomas and leukemias.
Side effects: Besides for maybe discolouring urine, if it’s given in very high doses, it has the potential risk (2-4%) to cause permanent damage to the heart resulting in heart failure. This is more likely to occur in higher risk patients, such as older patients with additional comorbidities, like high blood pressure and diabetes. Though, sometimes your oncologist will ask a cardiologist to see you before this drug is administered. There is a lifetime dose limit on these drugs, so if you have received it once, it will not be given to you again.
Examples: bleomycin and mitomycin C.
What cancers they treat: Hodgkin’s lymphoma and testicular cancer (bleomycin) and anal cancers (mitomycin C).
Side effects: A specific side effect for bleomycin is a long-term risk (10%) of developing scarring of the lungs, called pulmonary fibrosis. Mitomycin C can rarely cause a blood disorder, called haemolytic uraemic syndrome (<15%).
This group is divided into: topoisomerase I and topoisomerase II.
Examples: topotecan and irinotecan (topoisomerase I) and etoposide (topoisomerase II).
How they work: interfere with specific enzymes, called topoisomerases. These normally help separate strands of DNA so that they can be copied.
What cancers they treat: certain leukaemias, lung and gastrointestinal cancers.
Side effects: Topoisomerase II inhibitors can increase the risk (2-3%) of secondary myeloid leukaemia earlier in life (up to three years after treatment) than the alkylating agents.
The last group of chemotherapies is derived from natural products, such as plants and tree barks.
Examples: docetaxel, paclitaxel and vincristine.
How they work: stop the formation of new cells by stopping the cells from dividing. They can damage cells in all phases by keeping enzymes from making proteins that help cells to reproduce.
What cancer they treat: almost all cancer types.
Side effects: They can cause peripheral neuropathies which may be temporary but can also be permanent. This often limits how much of these drugs can be given for treatment.
There are other chemotherapy drugs that don’t fit into these specific groups. So, if you’re not sure, ask your oncologist. It’s important to know what treatment you’re receiving so that you can empower yourself by understanding your treatment, and to prepare and decrease your chances of getting specific side effects.
Drugs used together with chemotherapy
An integral part of chemotherapy treatment is corticosteroids. They are often used together with chemotherapy, as they’re effective in treating cancer but also help to prevent nausea and vomiting and even allergic reactions to chemotherapy drugs.
Examples: dexamethasone (Decadron), prednisone or methylprednisolone (Solu-medrol).
General side effects of chemotherapies
General side effects of all chemotherapy agents are:
- Fatigue, which is multi-factorial, for example, if you’re anaemic or simultaneously receiving radiation.
- Alopecia (hair loss) is a very distressing side effect but not all chemotherapies cause this.
- Low white blood cells can lead to infections.
- Sexual dysfunction, mucositis (inflamed lining of the mouth, mouth ulcers or sores), diarrhoea or constipation, skin changes or rashes, nausea and vomiting.
- Chemo brain (cognitive changes or memory loss) is also a real thing.
MEET OUR EXPERT – Dr Ronwyn van Eeden
Dr Ronwyn van Eeden is a medical oncologist at the Medical Oncology Centre of Rosebank. She has a special interest in supportive care in cancer and new anticancer agents, especially immunotherapy.