Cancer Chemotherapy - Toxic Agents
Chemotherapy drugs are toxic substances; they would not be effective in killing tumor cells if they were not. Although aimed at rapidly dividing tumor cells, they can also affect normal, healthy cells. This can cause unwanted side-effects for cancer patients. Some of the induced conditions will eventually return to normal, but other effects can be permanent. The long-term side-effects of chemotherapy will depend on the type of cancer, the drug treatment (intensity and rounds of therapy), age, sex and other health factors.
Fatigue and Reduced Immunity
Cancer chemotherapy can cause bone marrow suppression. Bone marrow is the dividing tissue in the centre of our bones which gives rise to our red and white blood cells. Bone marrow toxicity is seen particularly when patients require high intensity chemotherapy. This is usually seen during the course of treatment, but effects can last for several months afterwards.
- Red Cell effects: anemia - hindering the oxygen capacity of the blood and resulting in fatigue.
- White Cell effects: reduced white cell numbers - reduced immunity, hence making patients vulnerable to infection.
One of the long-term side effects of chemotherapy can be infertility. It may only be temporary, but in many cases may be permanent. Patients are often given the option of sperm banking or egg storage prior to the start of chemotherapy. In the future it may be possible to cryopreserve ovarian tissue (for re-implantation after treatment) but this is still at the experimental stage. Couples affected by cancer have the possible option of freezing fertilized embryos.
This is a generally considered to be a small risk. Some chemotherapy agents are capable of inducing mutagenic change in DNA, which years in the future can give rise to new cancers. The most common example of this is increased risk of acute myeloid leukaemia (AML) after treatment with alkylating agents or topoisomerase inhibitors, agents which are often used to treat breast cancer.
This is an increasingly recognised problem in cancer care. Many chemotherapeutic agents affect the cardiovascular system and cardiac disorders can appear several years after treatment. The pathological mechanisms vary between drugs, but in basic terms chemotherapy agents can cause heart disease by :
- Direct damage to the heart e.g. inflammation of the pericardium
- Affecting the blood coagulation system e.g increasing the risk of clot formation.
Oncologists will carefully assess a patient with a history of heart disease when determining cancer treatment. It is sometimes possible for cardio protective treatment to be given, so limiting the chemotherapy induced damage.
Some chemotherapy drugs e.g. bleomycin can cause inflammatory reactions in the lung. This generally ceases when the drug is halted, but in some cases the lung damage may not resolve, manifesting as a cough or breathlessness.
Cardiotoxicity of Anticancer Drugs: The Need for Cardio-Oncology and Cardio-Oncological Prevention, A.Albini et al. Journal of the National Cancer Institute, 2010, Vol 102, P14-25.
Acute Myelogenous Leukemia and Myelodysplasia Secondary to Breast Cancer Treatment: Case Studies and Literature Review, M.Cole & R.Strair. The American Journal of the Medical Sciences, 2010, Vol 339(1), P36-40.