Malignant: Definition and Characteristics

What is a Malignant Tumor?

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

What is the definition of the term malignant, and how does this differ from a process or tumor which is benign? What are the primary similarities and differences between malignant and benign tumors and why is it sometimes difficult to tell the difference?

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.

What are 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 (How They are Different Than Benign Tumors)

Malignant or cancerous tumors differ from benign tumors in several ways. Some of 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 crab or 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 (roughly 90 percent) 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 may recur locally (as with benign tumors,) regionally (for example, in lymph nodes near the original tumor,) or distantly (in organs or regions far from 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.) They also differ in their ability to spread (they lack "adhesion molecules" which keep normal cells in place, the way in which the cells communicate with each other, in their growth, and ultimately in their immortality or lack of cell death over time. 

    Ways in 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. Benign tumors can also be disfiguring depending upon their location.
    • 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, whereas benign tumors will only recur in the location where they were initially found.

    Why is Sometimes Difficult to Distinguish Benign and Malignant Tumors?

    If your doctor isn't certain whether a tumor is benign or malignant you may be surprised. Isn't this obvious? On scans such as a CT scan, MRI, or even PET scan, benign and malignant tumors can sometimes look very similar. Yet it can sometimes be difficult to tell the difference even under the microscope. While there are many differences between cancer cells, precancerous cells, and normal cells there is also a lot of overlap. In addition, in many tumors, there is a mixture of normal, precancerous, and cancer cells. Even among cancer cells, there can be differences in the appearance of these cells in different parts of a tumor (something referred to as "heterogenicity.")

    Pronunciation: mu-leeg-nant

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

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