How do cancers grow and spread?

If left untreated, cancers often go through three stages. They:

• Begin with one cell which has become cancerous. This divides and multiplies to form a 'primary tumour'. The tumour grows to invade the local surrounding tissue.
• At some point, some cancer cells may get into local lymph channels. (The body contains a network of lymph channels which drains the fluid called lymph which bathes and surrounds the the body's cells.) The lymph channels drain lymph into lymph nodes (sometimes called lymph glands). There are many lymph nodes all over the body. One or more cancerous cells may be carried to a lymph node and there become trapped. The cancerous cells then multiply and develop into a tumour within the lymph node. This is why lymph nodes that are near to a tumour may enlarge and contain cancerous cells.
• At some point, the cancer may spread to other areas of the body. (Some cancer cells may get into a local small blood vessel. They may then get carried in the bloodstream to other parts of the body. The cells may then multiply to form 'secondary' tumours (metastases) in one or more parts of the body. These secondary tumours may then grow and invade nearby tissues, and spread again.)

Each type of cancer differs in the speed in which these stages occur. For example, some cancers spread to local lymph nodes or to other parts of the body easily and quickly, even from a small primary tumour. By the time some cancers are diagnosed they have already spread to one or more sites in the body. On the other hand, some cancers grow slowly and remain in the primary site for months or years before they spread.

See separate leaflet called 'What are Cancers and Tumours' for more details.

What is cancer staging?

Staging is a way of describing how much a cancer has grown and/or spread. A common way of staging cancer is called the TNM classification. This records:

• T stands for tumour - how far the primary tumour has grown locally.
• N stands for nodes - if the cancer has spread to the local lymph nodes.
• M stands for metastases - if the cancer has spread to other parts of the body.

When a cancer is staged, a number is given for each of these three characteristics. For example, in stomach cancer:

• T-1 means the primary tumour is still in the stomach wall. T-3 means the primary tumour has grown right through the stomach wall and T-4 means it is invading nearby structures such as the pancreas.
• N-0 means there is no spread to lymph nodes. N-1 means that some local lymph nodes are affected. N-2 means more extensive spread to local lymph nodes.
• M-0 means there are no metastases. M-1 means that there are metastases to some other area of the body such as the liver or brain.

So, for a certain case of stomach cancer, a doctor may say something like "the stage is T-3, N-1, M-0" which means "the cancer has spread through the stomach wall, there is some spread to local lymph nodes, but no metastases in other parts of the body". 医学全在线www.med126.com

There are other staging classifications which are sometimes used for various cancers. For example, a common staging classification for bowel cancer (colorectal cancer) is called the Dukes Classification. This is:

• Duke A: the cancer is just in the inner lining of the colon or rectum.
• Duke B: the cancer has grown to the muscle layer in the wall of the colon or rectum.
• Duke C: the cancer has spread to at least one lymph node near to the colon or rectum.
• Duke D: the cancer has spread to other parts of the body ('metastases' or secondary tumours).

A number system is used for some cancers. That is, a cancer may simply be said to be stage 1, 2, 3 or 4 (or stage I, II, III, or IV). Again, the stages reflect how large the primary tumour has become, and whether the cancer has spread to lymph nodes or other areas of the body. It can become complicated as each number may be sub-divided into a, b, c, etc. For example, you may have a cancer at stage 3b. A grade 4 stage is often referred to as an 'advanced' cancer.

Why are cancers staged?

By finding the stage of a cancer it:

• helps doctors to advise on what is the best treatment.
• gives a reasonable indication of outlook (prognosis).
• describes the cancer in a standard language (a kind of shorthand language) which is useful when doctors discuss patients, and when patients are involved in clinical trials.

For example, if you have bowel cancer and it is diagnosed in an early stage then surgery to remove the tumour may be curative. (That is, if the cancer is confined to the lining of the bowel, with no spread to lymph nodes or to other parts of the body.) However, if the cancer is in a later stage, the primary tumour may or may not be able to be removed, treatment may also involve chemotherapy, and the chance of a cure is reduced.

How are cancers staged?

After a cancer is first diagnosed, to get an accurate staging you may need various tests. The tests can vary depending on the cancer but may include blood tests and scans such as CT scan, MRI scan, bone scan, ultrasound scan, etc. You may even need an operation to look inside part or parts of your body.

Sometimes a cancer cannot be accurately staged until after an operation has been done to remove the primary tumour. The tissues removed with the tumour are examined under a microscope to see how far the cancer cells have grown through the normal tissues, and whether the nearby lymph nodes contain cancer cells. There are separate leaflets which give details on the various scans and tests which may be advised to stage a cancer.

What is cancer grading?

Some cancers are also graded. A sample of the cancer (a biopsy) is looked at under the microscope. By looking at certain features of the cells the cancer can be graded as low, intermediate or high grade.

• Low grade means the cancer cells tend to be slow growing, look quite similar to normal cells (are 'well differentiated'), tend to be less 'aggressive', and are less likely to spread quickly.
• Intermediate grade is a middle grade.
• High grade means the cancer cells tend to be fast growing, look very abnormal (are poorly differentiated'), tend to be more 'aggressive', and are more likely to spread quickly.

Some cancers have a slightly different system of grading. For example, breast cancers are graded 1, 2 or 3 which is much the same as low, intermediate and high grade. Another example is prostate cancer which is graded by a Gleason Score. This is similar to other grading systems with a low Gleason score meaning much the same as 'low grade', and a high Gleason score meaning much the same as 'high grade'.

For some cancers, a doctor will use the information about the grade as well as the stage of the cancer when advising about treatment options, and when giving an opinion about outlook (prognosis).