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Benign vs Malignant Tumors

Diagram of a benign and malignant tumor
Credit: Technology Networks
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Tumors are abnormal masses of tissue formed when cells either grow too much or do not die when they should.1 Tumors are classified as one of two types – either benign (non-cancerous) or malignant (cancerous).2

In this article, we will describe what benign and malignant tumors are, explore the similarities and differences between the two types of tumors and discuss if benign tumors can become malignant.

What is a tumor?

Tumors are clusters of abnormal cells, and the word tumor comes from the Latin tumere – meaning “to swell”. The names of different types of tumors often end with the suffix “-oma”.

Usually, cells divide and proliferate under tightly controlled conditions, balanced by the programmed death of cells (known as apoptosis). However, mutations can occur in cellular DNA that affect this balance. These mutations can be random or caused by specific factors such as tobacco smoking or exposure to radiation.

If cells divide too much, or not enough cells undergo apoptosis, groups of cells can grow uncontrollably and produce a tumor. Tumors vary widely in size and can develop almost anywhere in the body.

People often associate tumors with cancer. However, some tumors are cancerous (malignant) and others are non-cancerous (benign). But what is the difference between a benign and malignant tumor?

What is a benign tumor?

Benign tumors are non-cancerous and generally less harmful than malignant tumors. They can grow to large sizes – potentially causing pain and other problems by putting pressure on the area around the tumor – but do not invade other tissues or organs.

They remain in their primary location, growing slowly and maintaining distinct borders around the edge of the tumor, and are unlikely to recur if they are surgically removed.

There are many types of benign tumors, including:

  • Adenomas – Develop in epithelial tissue, the thin layer of cells that cover and line structures such as glands and organs. The colon is commonly affected by adenomas.3
  • Fibroids – These grow from fibrous tissue such as the uterus. Between 20–80% of women will develop fibroids by 50 years of age.4
  • Hemangiomas – An abnormal growth of extra blood vessels.5 These mostly occur in the liver and under the skin, commonly appearing in children as a red birthmark.6
  • Lipomas – Occur in fatty tissue anywhere in the body – typically around the neck, shoulders, armpits and trunk. Mostly occur at age 40–60.7

What is a malignant tumor?

Malignant tumors are cancerous, with the capacity to spread and establish new tumors in other tissues and organs in a process called metastasis. During metastasis, primary malignant tumors spread to secondary sites. Cancer cells break away from the tumor and spread via the blood or lymph system – commonly establishing metastases in the liver, lungs, brain and bones.

Because of this, malignant tumors quickly require treatment to avoid spreading. Treatment usually entails surgical removal, chemotherapy, radiotherapy or a combination of these depending on how advanced the cancer is.

There are several established characteristics or “hallmarks” of cancer, such as inducing the production of new blood vessels (angiogenesis) and sustaining growth-promoting cell signaling.8,9,10,11

There are many types of malignant tumors.


Carcinomas develop in epithelial cells and are the most common type of cancerous tumor, representing 80–90% of cancers.12

Examples include:

  • Adenocarcinoma
  • Squamous cell carcinoma
  • Basal cell carcinoma
  • Transitional cell carcinoma


Sarcomas develop from cells in connective tissues such as bone, cartilage, fat, muscle, tendons and ligaments.

Examples include:

  • Osteosarcoma (bone)
  • Chondrosarcoma (cartilage)
  • Liposarcoma (fat)
  • Rhabdomyosarcoma (skeletal muscle)


These are cancers in immature precursor cells known as “blasts”. These malignant tumors are more common in children and are also referred to as embryonal malignancies as they are thought to occur after genetic errors in fetal cell development.13 Each kind of blastoma is named according to its tissue of origin in the body.

For example:

  • Glioblastoma – Astrocytes that support nerve cells within the brain and spinal cord.
  • Retinoblastoma – The light-sensitive cells of the retina in the back of the eye.
  • Hepatoblastoma – Occurs in liver cells, commonly in the right lobe of the liver.14

What’s the difference between benign and malignant tumors?

The major difference between benign and malignant tumors is their ability to spread and invade other tissues. Benign tumors can grow to a large size, but do not expand into other tissues or other areas of the body. Malignant tumors, on the other hand, are more aggressive.

These can invade neighboring tissues or even spread through the blood and lymph systems to distant parts of the body. New tumors that form in this way are called neoplasms, coming from the Greek “neo” meaning new, and “plasma” meaning formation.

A graphic illustrating the differences in the morphology of benign and malignant tumors. There are two pictures of tumors, one that is benign and the other malignant.

Figure 1: Graphic illustrating the differences in the morphology of benign and malignant tumors. Credit: Technology Networks.

The main differences between benign and malignant tumors are summarized in the table below:

Benign tumors

Malignant tumors





Not typically life-threatening

Can be life-threatening

Don’t invade nearby tissue, not attached to deep tissue structures

Able to invade nearby tissue, and attach to deep tissue structures

Do not spread to other parts of the body

Do spread (metastasize) to other parts of the body

Normally do not recur after removal

Often recur after removal

Distinct, regular shape

Irregular shape

Typically capsulated


May or may not need treatment

Require treatment

Cells are generally well-differentiated (normal appearance)

Cells can be poorly differentiated (abnormal appearance)

Doctors can determine whether a tumor is benign or malignant by taking a biopsy – a small sample of the tumor tissue – to examine under the microscope.

Can a benign tumor become malignant?

In some cases, benign tumors can indeed become malignant. Benign tumors can develop into a third, intermediate type of tumor known as "pre-malignant" or "pre-cancerous".

These growths remain benign but contain abnormal cells that have the potential to become cancerous in the future. One example of a pre-malignant tumor is known as carcinoma in situ.15 This is where abnormal cells are formed but have remained in place and not yet spread. However, they have the potential to spread into nearby tissue – for this reason, they are sometimes called “stage 0” cancer.16

Pre-malignant cells have several key characteristics that distinguish them from normal cells. These are:

  • Hyperplasia – An increased number of cells in an area of tissue, caused by an increase in cell division/proliferation.17
  • Dysplasia – Cells have an abnormal size/shape/appearance when observed under the microscope. This can be mild to severe depending on the degree of abnormality.18
  • Metaplasia – Cells look normal but are of the wrong cell type for that part of the body i.e., one cell type has been transformed into another cell type.19

One of the best examples of pre-malignant tumors are colon polyps – another name for small, abnormal growths. These polyps can be found during a colonoscopy (an examination using a camera to capture images of the inside of the colon). Some of these polyps have the potential to become pre-malignant and then malignant, requiring them to be closely monitored and possibly surgically removed.