Malignant - Definition and Characteristics

What is a Malignant Lung Tumor?

diagram of malignant cells
What is the definition of the term malignant?.

Definition: Malignant

In medicine, the word malignant is a term referring to a condition that is dangerous to health. While it is often used interchangeably with cancer, the term is also used to describe medical conditions outside of cancer than are dangerous or ominous. In other words, not all malignant conditions are cancerous. For example, we use the phrase malignant hypertension to describe blood pressure that is dangerously high, but in this context, it has nothing to do with cancer.

Likewise, the condition malignant hyperthermia describes an emergency situation in which a dangerously high fever develops during surgery with general anesthesia.

Malignant Tumors

A malignant tumor (cancerous tumor) is one that is invasive and can spread to other parts of the body. In contrast, tumors that stay localized and don't spread are called benign. Benign tumors may grow quite large and can do damage, but they do not usually spread through the bloodstream or lymph vessels to other parts of the body.  

Characteristics of Malignant Tumors

Cancerous tumors differ from benign tumors in several ways.  These include:

  • Invasion of nearby tissues - Malignant tumors have poor boundaries.  Unlike benign tumors which can press on nearby structures, malignant tumors can penetrate into nearby structures. The term "cancer" comes from the word claw, which refers to these finger-like projections invading tissues near the tumor.
  • Ability to spread (metastasize) - Unlike benign tumors, malignant tumor cells have the ability to break away from the tumor and travel, either locally, or through the bloodstream or lymphatic system. Most deaths from cancer occur due to this ability of malignant tumors to spread. Learn more about Most deaths from cancer occur due to this ability of malignant tumors to spread. Learn more about how cancer spreads.)
  • Likelihood and location of recurrence - Benign tumors may recur after removal, in the region where they were first located. In contrast, malignant tumors recur more often, and frequently in regions of the body that are distant to the original tumor.
  • Cells - There are many important differences between cancer cells and the cells found in a benign tumorCancer cells differ in their stickiness (attachment to surrounding cells) in the communication that occurs between cells, their growth, and in immortality (l

Ways Which Benign and Malignant Tumors are Alike

Some ways in which benign and malignant tumors are similar include:

  • Size - Both benign and malignant tumors can grow to be quite large.  For example, uterine fibroids, a benign tumor, can grow to become as large as a basketball.
  • Ability to cause damage - When benign tumors occur in the closed space of the brain, they can be very damaging, even though they do not spread to other regions of the body.
  • Local recurrence - Both benign and malignant tumors may come back after they are treated.  The difference is that malignant tumors may come back in different regions of the body to which they have spread.

Pronunciation: mu-leeg-nant

Examples: Rodney was saddened to learn his tumor was malignant and he would have to go through treatment for cancer.


U.S. National Library of Medicine. MedlinePlus. Malignancy. Updated 08/31/14.

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