Our bodies are made up trillions of cells. Normally, new cells replace old or damaged cells as they die off.

Sometimes, a cell’s DNA becomes damaged. The immune system can generally control a small number of abnormal cells from further damage to our bodies.

Cancer occurs when there are more abnormal cells than the immune system can handle. Instead of dying, abnormal cells continue to grow and divide, piling up in the form of tumors. Eventually, that out-of-control growth causes the abnormal cells to invade surrounding tissues.

There are more than 100 types of cancer named for the tissues or organs where they originate. All have the ability to spread, but some are more aggressive than others.

Continue reading to learn how cancer spreads, how it’s staged, and how various treatments work.

Cancer cells don’t respond to signals telling them it’s time to die, so they continue rapidly dividing and multiplying. And they’re very good at hiding from the immune system.

When cancer cells are still contained in the tissue where they developed, it’s called carcinoma in situ (CIS). Once those cells break outside the tissue’s membrane, it’s called invasive cancer.

The spread of cancer from where it started to another place is called metastasis. No matter where else in the body it spreads, a cancer is still named for the place it originated. For instance, prostate cancer that has spread to the liver is still prostate cancer, not liver cancer, and treatment will reflect that.

While solid tumors are a feature of many types of cancer, that’s not always the case. For example, leukemias are cancers of the blood that doctors refer to as “liquid tumors.”

Exactly where cancer cells will spread next is dependent on their location in the body, but it’s likely to spread nearby first. Cancer can spread through:

  • Tissue. A growing tumor can push through surrounding tissues or into organs. Cancer cells from the primary tumor can break away and form new tumors nearby.
  • The lymph system. Cancer cells from the tumor can enter nearby lymph nodes. From there, they can travel the entire lymph system and start new tumors in other parts of the body.
  • The bloodstream. Solid tumors need oxygen and other nutrients to grow. Through a process called angiogenesis, tumors can prompt the formation of new blood vessels to ensure their survival. Cells can also enter the bloodstream and travel to distant sites.

Cancer cells that have more genetic damage (poorly differentiated) usually grow faster than cancer cells with less genetic damage (well differentiated). Based on how abnormal they appear under a microscope, tumors are graded as follows:

  • GX: undetermined
  • G1: well-differentiated or low-grade
  • G2: moderately differentiated or intermediate-grade
  • G3: poorly differentiated or high-grade
  • G4: undifferentiated or high-grade

Some cancers that are generally slower growing are:

Some cancers, such as prostate cancer, can grow so slowly that your doctor may recommend a “watchful waiting” approach rather than immediate treatment. Some may never require treatment.

Examples of fast-growing cancers include:

Having a fast-growing cancer doesn’t necessarily mean you have a poor prognosis. Many of these cancers can be effectively treated. And some cancers don’t necessarily grow faster, but are less likely to be detected until they have metastasized.

Cancers are staged according to tumor size and how far it has spread at the time of diagnosis. Stages help doctors decide which treatments are most likely to work and give a general outlook.

There are different types of staging systems and some are specific to certain types of cancer. The following are the basic stages of cancer:

  • In situ. Precancerous cells have been found, but they haven’t spread to surrounding tissue.
  • Localized. Cancerous cells haven’t spread beyond where they started.
  • Regional. Cancer has spread to nearby lymph nodes, tissues, or organs.
  • Distant. Cancer has reached distant organs or tissues.
  • Unknown. There’s not enough information to determine the stage.


  • Stage 0 or CIS. Abnormal cells have been found but have not spread into surrounding tissue. This is also called precancer.
  • Stages 1, 2, and 3. The diagnosis of cancer is confirmed. The numbers represent how large the primary tumor has grown and how far the cancer has spread.
  • Stage 4. Cancer has metastasized to distant parts of the body.

Your pathology report may use the TNM staging system, which provides more detailed information as follows:

T: Size of primary tumor

  • TX: primary tumor can’t be measured
  • T0: primary tumor can’t be located
  • T1, T2, T3, T4: describes the size of the primary tumor and how far it may have grown into surrounding tissue

N: Number of regional lymph nodes affected by cancer

  • NX: cancer in nearby lymph nodes can’t be measured
  • N0: no cancer is found in nearby lymph nodes
  • N1, N2, N3: describes the number and location of lymph nodes affected by cancer

M: Whether cancer has metastasized or not

  • MX: metastasis can’t be measured
  • M0: cancer hasn’t spread to other parts of the body
  • M1: cancer has spread

So, your cancer stage might look something like this: T2N1M0.

Benign tumors

Benign tumors are noncancerous. They’re covered with normal cells and aren’t able to invade nearby tissue or other organs. Benign tumors can cause a few problems if they:

  • are large enough to press on organs, cause pain, or are visually bothersome
  • are located in the brain
  • release hormones that affect body systems

Benign tumors can usually be surgically removed and are unlikely to grow back.

Malignant tumors

Cancerous tumors are called malignant. Cancer cells form when DNA abnormalities cause a gene to behave differently than it should. They can grow into nearby tissue, spread through the bloodstream or lymph system, and spread through the body. Malignant tumors tend to grow faster than benign tumors.

Generally speaking, it’s easier to treat cancer before it has the chance to spread. Treatment depends on the specific type of cancer as well as the stage. In many cases, treatment will consist of more than one therapy.


Depending on the type of cancer you have, surgery may be the first-line treatment. When surgery is used to remove a tumor, the surgeon also removes a small margin of tissue around the tumor to lower the chances of leaving cancer cells behind.

Surgery can also help stage the cancer. For example, checking the lymph nodes near the primary tumor can determine if cancer has spread locally.

You may also need chemotherapy or radiation therapy following surgery. This may be an added precaution in case any cancer cells were left behind or have reached the blood or lymph system.

If a tumor can’t be completely removed, your surgeon may still remove part of it. This can be helpful if the tumor was causing pressure on an organ or causing pain.

Radiation therapy

Radiation uses high-energy rays to kill cancer cells or slow their growth. The rays target a specific area of the body where cancer has been found.

Radiation can be used to destroy a tumor or to relieve pain. It can also be used after surgery to target any cancer cells that may have been left behind.


Chemotherapy is a systemic treatment. Chemo drugs enter your bloodstream and travel throughout your body to find and destroy rapidly dividing cells.

Chemotherapy is used to kill cancer, slow its growth, and reduce the chance that new tumors will form. It’s useful when cancer has spread beyond the primary tumor or if you have a type of cancer for which there are no targeted therapies.

Targeted therapy

Targeted therapies depend on the specific type of cancer, but not all cancers have targeted therapies. These drugs attack specific proteins that allow tumors to grow and spread.

Angiogenesis inhibitors interfere with the signals that allow tumors to form new blood vessels and continue growing. These medicines can also cause already existing blood vessels to die, which can shrink the tumor.

Some types of cancer, like prostate and most breast cancers, need hormones to grow. Hormone therapy can stop your body from producing the hormones that feed the cancer. Others stop those hormones from interacting with cancer cells. Hormone therapy also helps to prevent recurrence.


Immunotherapies boost the power of your own body to fight cancer. These drugs can strengthen your immune system and help it recognize cancer cells.

Stem cell or bone marrow transplant

A stem cell transplant, sometimes called bone marrow transplant, replaces damaged blood-forming cells with healthy ones. The procedure takes place following large-dose chemotherapy or radiation therapy to kill cancer cells and to stop your stem cells from producing cancerous cells.

Stem cell transplants can be used for several types of cancer, including multiple myeloma and some kinds of leukemia.

Cancer isn’t a single disease. There are many types — and subtypes — of cancer. Some are more aggressive than others, but there are many variables that lead to different cancer characteristics.

Your oncologist can give you a better understanding of the typical behavior of a certain kind of cancer based on the specifics of your pathology report.