What Is the Difference Between a Malignant and a Benign Tumor?

One diagnosis signals cancer, while the other doesn't

Dividing cancer cell
Dividing cancer cell. STEVE GSCHMEISSNER/Science Photo Library/Getty Images

If you have been diagnosed with a tumor, the first step your doctor will take is to find out whether it is malignant or benign, as this will affect your treatment plan. In short, malignant means cancerous and benign means noncancerous. Learn more about how either diagnosis affects your health.

What Is a Tumor?

A tumor is an abnormal lump or growth of cells. When the cells in the tumor are normal, it is benign.

Something just went wrong, and they overgrew and produced a lump. When the cells are abnormal and can grow uncontrollably, they are cancerous cells, and the tumor is malignant.

To determine whether a tumor is benign or cancerous, a doctor can take a sample of the cells with a biopsy procedure. Then the biopsy is analyzed under a microscope by a pathologist, a doctor specializing in laboratory science.

Benign Tumors - Noncancerous

If the cells are not cancerous, the tumor is benign. It won't invade nearby tissues or spread to other areas of the body (metastasize). A benign tumor is less worrisome unless it is pressing on nearby tissues, nerves, or blood vessels and causing damage. Fibroids in the uterus or lipomas are examples of benign tumors.

Benign tumors may need to be removed by surgery. They can grow very large, sometimes weighing pounds. They can be dangerous, such as when they occur in the brain and crowd the normal structures in the enclosed space of the skull.

They can press on vital organs or block channels. Also, some types of benign tumors such as intestinal polyps are considered precancerous and are removed to prevent them becoming malignant. Benign tumors usually don't recur once removed, but if they do it is usually in the same place.

Malignant Tumors - Cancerous

Malignant means that the tumor is made of cancer cells and it can invade nearby tissues.

Some cancer cells can move into the bloodstream or lymph nodes, where they can spread to other tissues within the body—this is called metastasis. Cancer can occur anywhere in the body including the breast, intestines, lungs, reproductive organs, blood, and skin.

For example, breast cancer begins in the breast tissue and may spread to lymph nodes in the armpit if it's not caught early enough and treated. Once breast cancer has spread to the lymph nodes, the cancer cells can travel to other areas of the body, like the liver or bones. The breast cancer cells can then form tumors in those locations. A biopsy of these tumors might show characteristics of the original breast cancer tumor.

Differences Between Benign and Malignant Tumors

There are many important differences between benign and malignant tumors. Some of these include:

  • Growth rate: Malignant tumors may grow more rapidly than benign tumors, although there are slow-growing and fast-growing tumors in either category.
  • Ability to spread: Malignant tumors may spread to other parts of the body using the bloodstream or the lymphatic system. Malignant tumors may also invade nearby tissues and send out fingers into them, while benign tumors don't. Benign tumors only grow in the place where they started.
  • Recurrence: Benign tumors are easier to remove by surgery as they have clearer boundaries, and as a result, they are less likely to recur. If they do recur, it is only at the original site. Malignant tumors may have spread. As a result, they are more likely to recur and may recur in other sites, such as breast cancer recurring in the lungs or bones.
  • Cellular appearance: When a pathologist looks at tumor cells under a microscope, it is often obvious whether they are normal, benign cells or cancerous cells. Cancer cells often have abnormal chromosomes and DNA, making their nuclei larger and darker. They also often have different shapes than normal cells. However, sometimes the difference is subtle.
  • Systemic effects: While there are some benign tumors that secrete hormones, such as benign pheochromocytomas, malignant tumors are more likely to do so. Malignant tumors can secrete substances that cause effects throughout the body, such as fatigue and weight loss. This is known as paraneoplastic syndrome.
  • Treatments: A benign tumor can usually be completely treated with surgery, although some may be treated with radiation therapy or medication. Some benign tumors are not treated as they are not posing any health risk. Malignant tumors may require chemotherapy, radiation therapy, or immunotherapy medications to eliminate cells that may be remaining or may have spread to other parts of the body.

Can a Benign Tumor Turn Malignant?

Some types of benign tumors only very rarely transform into malignant tumors. But some types, such as adenomatous polyps (adenomas) in the colon have a greater risk of transforming into cancer. That is why polyps, which are benign, are removed during colonoscopy. Removing them is one way of preventing colon cancer.

It's not always clear-cut whether a tumor is benign or malignant, and your doctor may use several different factors to diagnose it as one or the other. You may end up with an uncertain diagnosis. Also, it is possible that a biopsy finds precancerous cells or misses the area where the cancerous cells are more prevalent. In these cases, what was thought to be benign might turn out to be malignant as it further grows and develops.

What Your Tumor Diagnosis Means

If you have been diagnosed with a malignant tumor, your oncologist (cancer doctor) will devise a treatment plan with you based on the stage of cancer. Early-stage cancers haven't spread much, if at all, whereas later-stage cancers have spread to more areas of the body. Determining the stage of cancer may require biopsies, surgery, and/or imaging tests. Once the cancer stage is determined, you can proceed with therapy.

If you have been diagnosed with a benign tumor, your doctor will provide reassurance that you do not have cancer. Depending on the type of benign tumor, your doctor may recommend observation or removal for cosmetic or health purposes (for instance, the tumor may be compromising an important organ in your body).

A Word From Verywell

Being diagnosed with a tumor can be an anxiety-ridden experience. Be sure to discuss your concerns with your doctor and ask whether there are any support groups that you can join. And remember, the earlier that you or your doctor detects a lump, the more likely the tumor is treatable. So if you notice something unusual on your body, don't wait to tell your doctor. 

Sources:

An, Y., Kim, S., and B. Kang. Differentiation of Malignant and Benign Breast Lesions: Added Value of the Qualitative Analysis of Breast Lesions on Diffusion-Weighted Imaging (DWI) Using Readout-Segmented Echo-Planar Imaging at 3.0 T. PLoS One. 2017. 12(3):e0174681.

Benign Tumors. National Institute of Health. MedlinePlus. Updated 07/07/16. https://medlineplus.gov/benigntumors.html

What are Tumors? Johns Hopkins Medicine. http://pathology.jhu.edu/pc/BasicTypes1.php

What is Cancer? National Cancer Institute. Updated 02/09/15. https://www.cancer.gov/about-cancer/understanding/what-is-cancer

What is Cancer?: A Guide for Patients and Families. American Cancer Society. Updated December 2015. https://www.cancer.org/cancer/cancer-basics/what-is-cancer.html.

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