How does chemotherapy fight cancer?

DEAR DOCTOR K:

My mother was diagnosed with cancer and will soon begin chemotherapy. I’d like to understand how chemotherapy is given, and how it fights cancer.

DEAR READER:

Chemotherapy uses drugs that kill cancerous cells, but only injure healthy cells. To understand chemotherapy, you need to understand what cancer is and what is different about cancer cells.

Our body contains 13 trillion cells. They all started from one cell, a cell that kept dividing. One cell became two, two became four, and so on. But the cells kept dividing in a carefully controlled manner. Early in our lives (even before we were born), they had to keep dividing so that we would grow larger. After we are fully formed adults, some cells need to divide to replace dying old cells with younger ones.

In contrast, cancer is the uncontrolled growth of abnormal cells. Chemotherapy (anti-cancer) drugs kill cancer cells or prevent them from growing and dividing. The drugs reach almost all parts of the body. This helps to kill cancer cells that have spread from the original site of the cancer.

Chemotherapy is the core treatment for some cancers. For other cancers, it is part of a larger strategy along with radiation and/or surgery. Chemotherapy often requires a combination of two or more different anti-cancer drugs. Cancer specialists (oncologists) design chemotherapy plans based on the cancer being treated and how far the cancer has spread.

Cancer chemotherapy may be designed to:

  • cure the cancer;
  • prevent the cancer from recurring after surgery;
  • prevent the cancer from spreading to other organs;
  • decrease the size of a tumor to make surgery easier;
  • shrink the size of incurable cancer to help relieve symptoms.

Chemotherapy drugs can be given in a hospital, clinic, doctor’s office or at home. For most people, a bag filled with the liquid drug is attached to a tube that is inserted into a vein. The drug slowly drips into the patient’s body. Sometimes the patient is able to swallow a pill instead, or get chemotherapy through an injection. People can receive chemotherapy daily, weekly or monthly.

Unfortunately, in addition to attacking cancer cells, chemotherapy drugs also injure normal, healthy cells. This can cause many side effects.

Many anti-cancer drugs, for example, affect the production of blood cells. This includes red blood cells that carry oxygen and platelets that help blood clot. Chemotherapy also inhibits the production of white blood cells that fight infection. That’s why a common side effect of chemotherapy is increased susceptibility to serious infections.

Other common side effects include fatigue, nausea and vomiting, diarrhea, mouth sores, hair loss and rashes. Your mother’s doctor can help manage many of these side effects.

In recent years, medical scientists have developed new treatments. Some target the chemical changes in cancerous cells that cause them to grow uncontrollably. Others harness the body’s immune system to attack cancerous cells. For certain types of cancers, these new approaches appear more effective, and less toxic, than chemotherapy.

(This column ran originally in November 2014.)