What Is Chemotherapy and How Does It Work?

Chemotherapy for cancer is drug therapy with chemicals that target cell growth, which can ideally keep cancer from growing and spreading or even sending it into full remission. Though the drugs have improved over the years, chemotherapy is still known for having severe side effects, depending on the drug cocktail and intensity of treatment.

Chemotherapy (“chemo”) refers to drugs that treat cancer or ease cancer symptoms. 

How Does Chemotherapy Work?

Chemotherapy drugs target cells at different phases of the cell cycle. The cell cycle is the process by which a new cell becomes a fully functioning (or mature) cell.

Cancer cells usually produce new cells more quickly than normal, but chemotherapy drugs can’t tell the difference between healthy cells and cancer cells. When chemotherapy is administered, normal cells are damaged along with the cancer cells, resulting in side effects. The goal of chemo is to find a balance between killing the cancer cells and sparing healthy cells.

There are different types of chemotherapy drugs that work differently to target cancer cells. 

• Alkylating agents 
  • Damage a cell’s DNA which prevents the cell from reproducing 
  • Works in all phases of the cell cycle and are used to treat many different cancers, including lung cancer, breast cancer, ovarian cancer, leukemia, lymphoma, Hodgkin disease, multiple myeloma, and sarcoma
  • Can affect the cells of bone marrow and in rare cases lead to leukemia
• Nitrosoureas 
  • A type of alkylating agent that can cross the blood-brain barrier (the other alkylating agents cannot)
  • Useful for treating certain types of brain tumors
  • Antimetabolites
  • Interfere with DNA and RNA by acting as a substitute for the normal building blocks of RNA and DNA so the DNA cannot copy itself, and a cell cannot reproduce
  • Used to treat leukemias, cancers of the breast, ovary, and the intestinal tract, and some other types of cancer
• Anti-tumor antibiotics
  • Not the same as antibiotics used to treat infections
  • They change the DNA inside cancer cells to prevent them from growing and multiplying
  • Anthracyclines interfere with enzymes involved in copying DNA during the cell cycle and are used for a variety of cancers
  • Can permanently damage the heart if given in high doses
• Topoisomerase inhibitors (also called plant alkaloids)
  • Interfere with enzymes called topoisomerases, which help separate strands of DNA so they can be copied 
  • Used to treat certain leukemias, along with lung, ovarian, gastrointestinal, colorectal, and pancreatic cancers
• Mitotic inhibitors (also called plant alkaloids)
  • Derived from natural products, such as plants
  • They stop cells from dividing to form new cells, but can damage cells in all phases by keeping enzymes from making proteins needed for cell reproduction
  • Used to treat many different types of cancer including breast, lung, myelomas, lymphomas, and leukemias. 
  • May cause nerve damage
• Corticosteroids
  • Natural hormones and hormone-like drugs used to treat many types of cancer, as well as other illnesses
  • Also used to help prevent nausea and vomiting caused by chemo and used before some types of chemo to help prevent severe allergic reactions
• Other chemotherapy drugs
  • There are additional chemotherapy drugs that act in slightly different ways and do not fit well into other categories

There are other types of drugs and biological treatments used to treat cancer that are not considered chemotherapy but may be used along with chemotherapy.

• Targeted therapies
  • Work by targeting specific proteins or receptors that some cancer cells have
  • Normal cells are not affected by these drugs
• Hormone therapy
  • Work on different actions of hormones that make some cancers grow, either by making the cancer cells unable to use the hormone they need to grow, or by preventing the body from making the hormone
  • Used to slow the growth of some breast, prostate, and endometrial (uterine) cancers
• Immunotherapy
  • Uses drugs to boost or alter a person's immune system
  • Used with certain types of cancer to help a patient's immune system recognize and attack cancer cells