What is a Benign Tumor?

A benign tumor is a tumor which tends to be less aggressive, less invasive in the body and slower growing. Benign tumors are not cancer. All cancers are malignant tumors.

The term benign comes from a Latin root meaning good or kind. While it is arguable that no tumor is "good" or "kind", compared to the more aggressive types of tumors, benign ones are relatively good. The "opposite" of benign would be a malignant tumor which in contrast tends to be more aggressive and invasive and faster 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.

Some types of benign growths, but not the majority, have the potential to undergo further mutations and eventually become malignant. This is termed malignant potential and the changing from benign to malignant is called malignant transformation.

Characteristics of Benign Tumors:

Less Invasiveness: As mentioned above, benign masses tend to be less aggressive and less invasive in the body. This means that the growing cells do not tend to invade directly into surrounding normal tissues. Instead, as they slowly grow they stick together and are separate from surrounding tissues. As they get large, they can cause damage to surrounding tissue but pushing it out of the way and causing pressure on it, but they do not directly invade into the tissue as malignant tumors do.

Slower Growing: Although the speed at which tumors grow and spread varies quite a bit, benign ones tend to grow slower. The cells typically don't divide as rapidly and therefore the tumors can grow quite slowly. In fact, some patients with benign tumors can harbor a tumor for many years or even decades without knowing it because it grows so slowly.

No Metastasis: Most malignant tumors have the ability to metastasize, which means that they can spread to distant organs in the body. Benign tumors, by definition, do not metastasize. They only spread by direct extention of the primary tumor. They do not spread in the bloodstream or lymphatics to distant organs.