Cancer cells vs. normal cells

This page was reviewed under our medical and editorial policy by

Bradford Tan, MD, Chair, Department of Pathology and Laboratory Medicine, City of Hope Atlanta, Chicago and Phoenix

This page was reviewed on November 15, 2021.

The human 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 out of control and continue to reproduce other abnormal cells. These cells invade body parts, such as the breast, liver, lungs and pancreas. They may also flow through the 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.

How are cancer cells different from normal cells?

The main difference between cancer cells and normal cells is that cancer cells grow uncontrollably. The body's immune system can't stop or kill them quickly enough to keep them from multiplying, which allows them to grow and sometimes spread.

By understanding how cancer cells differ from normal cells, researchers may develop treatments.

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

Cancer cells keep dividing. Cancer cells ignore the body’s signals to stop growing and multiplying. The body has a built-in process, called apoptosis (programmed cell death), that tells the body to get rid of cells it doesn’t need anymore. Normal cells are better at listening: They respond 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 the body metabolize proteins, fats and carbohydrates and help remove alcohol in the 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. Most people know that the immune system helps 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 the 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 do cancer cells form?

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

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

Patients inherit them from their 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.

Patients acquire them. Most cancers happen through acquired—or somatic—mutation. Instead of inheriting these mutations, they’re picked up throughout the person's life through environmental exposures. For example, smoking, secondhand smoke and ultraviolet rays from the sun may cause cancers by damaging DNA. When DNA is damaged, it may allow a cancer cell or small group of cancerous cells to grow, emerge and divide.

How is cancer diagnosed?

Though cancer cells may trick the body and hide, doctors have various ways to detect and diagnose cancer, including those listed below.

Laboratory tests. Cancer patients often have high or low levels of certain substances. Urine and blood tests may detect these substances. It’s important to note that having an abnormal test result doesn’t mean that a patient has cancer. The care team may contact the patient 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 the care team may use to detect cancer.

Biopsies. Doctors typically perform a biopsy to diagnose cancer. During a biopsy, the doctor removes a small sample of tissue. The tissue is examined under a microscope and goes through a series of tests. The care team 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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