What is a Malignant Tumor?

A malignant tumor is a tumor which tends to be more aggressive, invasive in the body and faster growing. The term malignant, when refering to a tumor, is synonymous with cancer. All cancers are malignant.

The term malignant comes from the Latin root mal- meaning bad. The "opposite" of malignant would be a benign tumor which in contrast tends to be less aggressive and invasive and slower growing.

All tumors fall on a spectrum in terms of their "personality". Some tumors are comprised of cells which are not that different from normal cells. These tumors are typically slower growing and less aggressive. Tumors on this end of the spectrum are termed benign. On the other hand, at the upper end of the spectrum are tumors which are made of very abnormal cells which are able to grow and divide at a faster rate. They tend to be faster growing and much more invasive and destructive of surrounding normal tissue. These tumors are termed malignant.

It is important to note, however, that there is no absolute middle point in this spectrum and therefore the determination of benign versus malignant is somewhat arbitrary. While there are certainly tumors on the far ends of the spectrum which are clearly benign or malignant, there are some near the middle of the spectrum. Therefore, some "benign" tumors can be relatively invasive and aggressive and some "malignant" tumors can be less aggressive than others.

In some cases, malignant tumors can evolve from a benign one. In other words, some types of benign tumors can undergo further mutations and eventually change into cancer. Not all benign tumors have this potential (termed malignant potential).

Characteristics of Malignant Tumors:

Invasiveness: As mentioned above, cancers tend to be more aggressive tumors. They are invasive in the body, meaning that they do not just sit in one place and slowly grow, pushing other things out of the way. Instead, they tend to invade directly into surrounding tissues and structures, often causing damage to the surrounding normal tissues as they grow. This invasiveness means that cancers tend to be harder to separate from surrounding normal tissues and can more quickly cause significant symptoms and tissue destruction.

Faster Growing: Although the speed at which tumors grow and spread varies quite a bit, malignant ones tend to grow faster. The very abnormal cells have the ability to divide quickly.

Metastasis: Most malignant tumors have the ability to metastasize, which means that they can spread to distant organs in the body. While the primary tumor invades surrounding tissues locally, they can also spread far away and start growing elsewhere in the body. This can occur either through the bloodstream or through the lymphatics. The metastases in other organs can continue to grow there, often causing symptoms related to that organ. Benign tumors do not metastasize.