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The information on this page was reviewed and approved by
Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was updated on June 10, 2021.

Cancer cells vs. normal cells

Your body constantly produces new cells. Normal cells follow a typical cycle: They grow, divide and die. Cancer cells, on the other hand, don’t follow this cycle. Instead of dying, they multiply and continue to reproduce other abnormal cells. These cells can invade body parts, such as the breast, liver, lungs and pancreas. They may also flow through your blood and lymphatic system and spread to other parts of the body.

Below, learn how cancer cells differ from normal cells, how they form, and how scientists examine cancer cells.

Key differences

By understanding how cancer cells differ from normal cells, researchers develop treatments. If you have cancer, this knowledge may help you understand what’s going on inside your body.

These are the most significant differences between cancer cells and normal cells:

  • Cancer cells keep dividing. Cancer cells ignore the body’s signals to stop dividing. Your body has a built-in process, called apoptosis or programmed cell death, that tells the body to get rid of cells it doesn’t need anymore. Normal cells are better at listening: They listen to the body’s cues and stop reproducing when enough cells are present.
  • Cancer cells grow too rapidly to mature. Normal cells mature into distinct cell types. These different cell types have specific functions. For example, liver cells help your body metabolize proteins, fats and carbohydrates and help remove alcohol in your blood. Cancerous cells divide so quickly that they don’t have a chance to mature and become the specialized cells they set out to be.
  • Cancer cells may influence normal cells. Cancer cells may actually affect the behavior of the normal cells, molecules and blood vessels near a tumor. For example, cancer cells may recruit normal cells to develop new blood vessels. These vessels keep the tumor alive—and give it a chance to grow—by providing it with oxygen and nutrients.
  • Cancer cells trick the immune system. You probably know your immune system helps you fight off infection and disease. The immune system typically gets rid of abnormal or damaged cells. Cancer cells manage to evade this process, which allows tumors to grow.
  • Cancer cells are invasive. Because cancer cells ignore the body’s signals to stop dividing, they start invading tissues nearby. If a tumor is benign, it may push up against neighboring tissues, but won’t invade it. However, a malignant tumor invades tissue and is capable of spreading throughout the body.
  • Cancer cells may spread to other parts of the body. Normal cells know their place in your body and stay put. Metastatic cancer cells start spreading to other parts of the body. For example, cancer may develop in the lungs and spread to the liver. If this spread occurs, it’s known as metastatic lung cancer, not liver cancer.

How cancer cells form

Hundreds of millions of cells make up your body. It’s normal for some of your cells to be abnormal, but your body has a series of processes to protect you from them. Cancer cells are evasive. They bypass your body’s internal buffers. But how do they do it?

It comes down to genetics. Genes control the way your cells divide and grow and when they die. Sometimes, a cell changes—or mutates—when it divides. Genetic changes to cells may happen if:

  • You’ve inherited them from your parents. Some cancers, such as breast cancer and ovarian cancer, run in families. The inherited gene mutation is in the egg or sperm at conception. The sperm fertilizes the egg and forms one cell. That cell divides, and the genetic mutation ends up in every single cell.
  • These mutations often happen in tumor suppressor genes, which typically help ensure cells divide and die at the right time. Tumor suppressor genes also fix DNA mistakes. But if there are inherited mutations in these tumor suppressor genes, that may not happen.
  • You acquire them. Most cancers happen through acquired—or somatic—mutation. Instead of inheriting these mutations, they’re picked up throughout your life through environmental exposures. For example, smoking, secondhand smoke and ultraviolet rays from the sun may cause cancers by damaging your DNA. When your DNA is damaged, it may allow a cancer cell or small group of cancerous cells to grow, emerge and divide.

How doctors detect cancer cells

Though cancer cells may trick your body and hide within them, doctors have various ways to detect and diagnose cancer, including:

  • Laboratory tests. Cancer patients often have high or low levels of certain substances. Blood and urine tests may detect these substances. It’s important to note that having an abnormal test result doesn’t mean you have cancer. Your doctor may talk to you about the findings and next steps.
  • Imaging tests. Computed tomography (CT) scans, magnetic resonance imaging (MRI) scans, ultrasounds, positron emission tomography (PET) scans, bone scans, X-rays and nuclear scans are some of the imaging tests your care team may use to detect cancer.
  • Biopsies. Doctors typically perform a biopsy to diagnose cancer. During a biopsy, your doctor removes a small sample of tissue. The tissue is examined under a microscope and goes through a series of tests. Your doctor may get a biopsy sample with a needle, through surgery, or through a procedure where a thin tube with a light and camera is inserted into the body. Tools may be sent through the tube in order to take a sample of tissue for testing.
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