Chemotherapy is a treatment for cancer that uses drugs to kill malignant cells or stop their growth. In contemporary cancer care, the term generally refers to conventional cytotoxic drugs, rather than every medicine used against cancer. These drugs interfere with processes needed for cellular reproduction and can also damage healthy tissues. Chemotherapy may be used alone or alongside other treatments, with the aim of curing cancer, controlling its growth, reducing recurrence, or relieving symptoms. Its effects depend on the disease, the drugs administered, and the individual receiving treatment. (cancer.org)
Biological basis
Many chemotherapy drugs act on processes associated with cell division. During the cell cycle, a cell grows, copies its DNA, and divides. Drugs can damage genetic material, interfere with its synthesis, or prevent the machinery of division from functioning. Some act mainly during particular phases of the cycle, whereas others can act across multiple phases. These differences help explain why drug selection and treatment timing vary between cancers. (cancer.org)
Chemotherapy does not exclusively affect cancer cells. Healthy cells that divide frequently—including cells associated with hair growth and the lining of the mouth and intestines—can also be injured. This limited selectivity accounts for several characteristic adverse effects. Different drugs affect these processes differently, so chemotherapy is not a single treatment with a uniform biological action. (cancer.org)
Major drug classes
Chemotherapy drugs are grouped by their mechanisms, chemical structures, and relationships to other agents. The classifications overlap: an individual drug may have more than one relevant action. Major groups include:
- Alkylating agents, such as cyclophosphamide, which damage DNA and impede cellular reproduction. Platinum drugs, including cisplatin and carboplatin, also damage DNA and are often grouped with alkylating agents, although they are chemically distinct.
- Antimetabolites, including methotrexate, fluorouracil, and cytarabine, which interfere with nucleic-acid synthesis and DNA replication.
- Antitumor antibiotics, including anthracyclines such as doxorubicin, which interfere with DNA and associated enzymes. Their anticancer role differs from that of antibiotics used against infections.
- Topoisomerase inhibitors, such as irinotecan and etoposide, which disrupt enzymes involved in managing DNA structure.
- Mitotic inhibitors, including taxanes and vinca alkaloids, which interfere with microtubules and processes required for mitosis. (cancer.org)
Clinical purposes and combinations
Chemotherapy is used for many solid tumors and blood cancers, including leukemia and lymphoma. Most conventional chemotherapy is systemic: drugs circulate through the bloodstream and can reach malignant cells beyond the original tumor. This differs from local treatments directed principally at a particular site, such as surgery and radiation therapy. (cancer.org)
Neoadjuvant chemotherapy is administered before surgery or radiation, often to shrink a tumor. Adjuvant chemotherapy follows local treatment to destroy malignant cells that may remain. Chemotherapy can also be used against recurrent or disseminated disease. When the purpose is symptom relief rather than cure, it may form part of palliative care, for example by shrinking a tumor that causes pain or pressure. (cancer.gov)
A regimen may contain several drugs with different mechanisms. Combinations can attack cancer cells in different ways, but their toxicities also influence regimen design. Cancer cells may become resistant to an agent, making subsequent treatment with different drugs necessary. (cancer.org)
Administration and scheduling
Common routes include intravenous infusion, oral tablets or liquids, and injections. Intravenous drugs may be delivered through a temporary catheter, a longer-term central venous catheter, or an implanted port. Infusion pumps can administer drugs over extended periods, sometimes outside a hospital. Other routes deliver chemotherapy into an artery, a body cavity, or cerebrospinal fluid. Intrathecal administration can reach areas around the brain and spinal cord that many systemically administered drugs do not readily enter. (cancer.org)
Treatment commonly proceeds in cycles: a period of drug administration is followed by a recovery interval. The schedule depends on the cancer, treatment objective, drugs, and response. Before infusions, clinical assessments may include blood counts, vital signs, and physical examination. Supportive medicines can include anti-nausea drugs, corticosteroids, and medicines that reduce infusion reactions. (cancer.gov)
Adverse effects
Possible short-term effects include fatigue, nausea, vomiting, mouth sores, diarrhea, constipation, and hair loss. Their occurrence and severity vary substantially; not every drug produces every effect. Chemotherapy can suppress blood-cell production in the bone marrow. Reduced red-cell production may cause anemia, while reduced white blood cell production can increase susceptibility to infection. (cancer.gov)
Some adverse effects persist after treatment or develop later. Depending on the drug and exposure, these can include heart damage, nerve damage, impaired fertility, and an increased risk of a second cancer. Many other effects improve after treatment ends. The severity of adverse effects is not a reliable measure of how effectively chemotherapy is controlling cancer. (cancer.org)
Assessment and distinctions from other therapies
Response is assessed through clinical examination, blood tests, and imaging, potentially including computed tomography or magnetic resonance imaging. The assessment method depends on the disease and treatment setting. (cancer.gov)
Conventional chemotherapy is distinguished from targeted therapy, which acts on specific molecular features, and cancer immunotherapy, which helps the immune system attack cancer. Hormone therapy blocks hormonal production or activity relevant to certain tumors. These treatments may be combined with chemotherapy but are not interchangeable categories. (cancer.org)