Chemotherapy. If you or someone you know has
been diagnosed with breast cancer, the chances are that you’ve
heard this word spoken in conversation. You may even have
an idea of what it entails, but what is it really? How does
it work, and how will it affect you or your loved one?
What is Chemotherapy?
The word chemotherapy means different things to different
people. To health care professionals, it refers to any chemical
or drug used to treat a symptom of an illness. However, the
general public tends to associate the word chemotherapy with
the drug treatment regimes specifically used for battling
Learning About Chemotherapy
While reading literature or talking to health care professionals
about chemotherapy for cancer treatment you may also come
across the terms antineoplastic and cytotoxic. These words
describe the way that chemotherapy drugs act to stop cell
replication or even lead to cell death. Additionally, adjuvant
chemotherapy is chemotherapy applied after surgery has taken
place in order to kill any cells that may have escaped the
surgery and entered the bloodstream. Neoadjuvant chemotherapy
refers to drug treatment used to reduce the size of a tumor
prior to beginning other treatments.
Uses of Chemotherapy
Chemotherapy is a widely used method of cancer treatment
primarily due to the fact that it is a systemic treatment.
It will affect the entire body. Chemotherapy drugs are usually
administered either orally or directly into a vein, which
means that they eventually end up traveling through the bloodstream
to all areas of the body. This is especially beneficial if
cancer has spread from its point of initiation, or metastasized.
How Chemotherapy Works
Drugs used in chemotherapy are effective primarily because
they stop cells from dividing. A normal, healthy cell goes
through a replication cycle that includes an internal growth
phase in which a second set of proteins, DNA and RNA are made,
and a division phase where via a process called mitosis the
cell splits in two. This cell division cycle continues until
internal controls make the cell stop replicating itself. These
controls are damaged or turned off in cancerous cells, so
cancerous cells continue dividing indefinitely. Anticancer
drugs affect cells at various points in their division cycle,
and block cellular instructions for cell division. Research
has led to the development of over 100 chemotherapy drugs
that affect different stages of the cell division cycle.
One group of drugs work as alkylating agents, and bind directly
to DNA at any stage in the cell cycle stopping it from being
replicated. Examples of some alkylating drugs used are busulfan,
cisplatin, carboplatin, chlorambucil, cyclophosphamide, ifosfamide,
dacarbazine (DTIC), mechlorethamine (nitrogen mustard), and
Nitrosoureas, like alkylating agents, block DNA replication,
but do so by affecting the enzymes involved instead of by
attaching to the DNA. These drugs are important due to their
ability to gain access to the brain’s blood supply.
Two of these drugs are called carmustine (BCNU) and lomustine
5-fluorouracil, capecitabine, methotrexate, gemcitabine,
cytarabine (ara-C), and fludarabine are members of a group
of drugs known as anti-metabolites. These drugs block DNA
and RNA replication during the growth phase of the cell cycle.
Some examples of drugs that stop mitosis directly or indirectly
through the inhibition of crucial reproduction enzymes are
paclitaxel, docetaxel, etoposide (VP-16), vinblastine, vincristine,
and vinorelbine. Interestingly, these drugs come from natural
sources and many are actually plant products.
There is also a class of antibiotics that works against tumor
growth. These drugs stop replication enzymes and mitosis,
and many affect the cell membrane itself to make cell division
impossible. Examples of these drugs include dactinomycin,
daunorubicin, doxorubicin (Adriamycin), idarubicin, and mitoxantrone.
Sex hormones such as anti-estrogens (tamoxifen, fulvestrant),
aromatase inhibitors (anastrozole, letrozole), progestins
(megestrol acetate), anti-androgens (bicalutamide, flutamide),
and LHRH agonists (leuprolide, goserelin) change the release
of male or female hormones in the body, and can affect the
growth and development of tumors, which are often hormone
responsive. Corticosteroid hormones like prednisone and dexamethasone
are sometimes also used to slow the growth rate of some cancers.
Immunotherapy drugs are widely used to stimulate the body’s
immune system to attack cancerous cells. There are several
compounds like L-asparaginase and tretinoin that do not fit
into any of the described categories, but have been shown
quite efficacious in treating some cancers. Doctors are able
to determine which drugs to use and in what combination based
upon the developmental stage of the cancer and personal factors
of the patient.
Most of the drugs named above are used in combination with
other drugs allowing a multifaceted attack that is specific
to the cancer and person being treated. In this way cancerous
cells can be stopped, however it is also at the expense of
any healthy cells that happen to be dividing as well. Unfortunately,
chemotherapy drugs are not specific to only cancerous cells,
but to any dividing cells. The death of healthy cells is what
leads to the undesirable side effects of chemotherapy such
as hair loss, nausea, vomiting, diarrhea, dry mouth, fatigue,
and reduced immune function.
Chemotherapy is one of many current treatments for most forms
of cancer. It is useful since it can be fine-tuned for each
independent patient, and new research is making more drugs
and therefore treatment possibilities available. If you have
been diagnosed with cancer, use the information that has been
included here to assist you in talking to your doctor about
determining the best treatment regimen for you.
Kirsten Sanford is a science journalist
& PhD candidate in the Molecular, Cellular and Integrative
Physiology Graduate Group at the University of California,
Davis. In addition to developing patient health education
materials she also hosts a weekly science radio show (This
Week in Science) dedicated to bringing current scientific
news and research to the public.