How do cancer cells grow and spread?

The human body is made up of billions of cells. Cells are the tiny building blocks of our tissues and organs. We all started life as a single cell. That cell made an internal copy of itself (replication) and then divided into two cells.

 

Illustration: Cell divisionCell division

Those two cells then also replicated and divided, so the two cells became four cells. The four cells replicated as well and divided into eight cells, and so on.

Cells specialize to perform particular tasks. Some cells will cluster together to form a finger, for example. Others create skin and heal the skin when it is wounded. Cells get old and die after a certain amount of time (“programmed cell death,” or apoptosis), and replication ensures that new cells are made to take their place.

When they are acting normally, cells “know” which other cells to join up with and stick to – and they also know when to stop replicating and die. Each type of cell has a particular role and set of knowledge or instructions in their DNA (genes). Our cells know how to make the right number of fingers on our hand for us (and they know that fingers should only grow on our hands).

Each finger is covered with skin and each finger has a fingernail. If we cut our finger, the skin cells will start replicating and create new skin to heal the wound. If we lose a fingernail, our cells can grow a new one. But the cells will not create extra fingers, even if we lose one. The rules are clear for those cells, and they keep to the rules.

The role of hormones and the lymphatic system

Our hormones carry messages to our cells, triggering the cells to take action. These messages are carried by our blood through our blood vessels. The blood carries the other things that cells need to function too. Our cells need oxygen and glucose to keep them alive, for example. Our blood vessels also carry away waste products and oxygen-poor blood once the cells have used the oxygen in the blood. Our lymphatic system helps to clean and get rid of what we don't need. The lymphatic system is a part of our body’s defense system (immune system), and it drains away bacteria and germs.Illustration: Normal cellsNormal cells

Benign and malignant growth

Cells become abnormal if their DNA – which carries the instructions they need – becomes damaged. Then the cells that come from them will be different from healthy cells. They look different, and they may also have different properties. If these kinds of abnormal cells grow in body tissue – such as skin, for example – it is referred to as dyplasia. As long as there are very few abnormal cells and they're kept under control by our immune system, they won't harm us. Sometimes these kinds of cells will also go away on their own. It is only when they keep on changing and start to divide uncontrollably, forming lumps or growths, that one of the more than 200 diseases called cancer develops. Growths like this are called tumors.

The main differences between malignant (cancerous) and benign (non-cancerous) tumors are that malignant ones can

  • spread into the surrounding tissue,
  • destroy the surrounding tissue, and
  • cause other tumors to develop.

Malignant tumors can be life-threatening. But there are also some kinds of cancer that develop so slowly in older people that they don't lead to any problems in their lifetime. Benign tumors usually don't cause much damage and aren't normally life-threatening. But there's no guarantee: Benign growths can become dangerous if they grow a lot, or they might become malignant after a certain amount of time.

If cancer cells start replicating, they don't behave like normal cells. For example, they don't know when to stop replicating and when to die. And they don't always stick together, so they might break away and move through the blood vessels or lymphatic system and start growing somewhere else in the body. This process is called metastasis. 

Illustration: Carcinoma in situCarcinoma in situ

When a malignant tumor is contained within one area and hasn't spread to the surrounding tissue, like the one in the picture above, the medical term is “carcinoma in situ.” If this tumor stops growing, doctors say it is dormant (“dormant cancer cells”).

These kinds of tumors start to create their own blood vessels so that they can continue to grow. The blood vessels supply them with extra oxygen, glucose (sugar) and hormones. This process of developing a blood supply system is called angiogenesis (the growth of new blood vessels). Once a tumor does this, it can start to invade the surrounding tissue. This is called invasive cancer, and you can see what that looks like below:Illustration: Invasive cancerInvasive cancer

Active cancer cells can enter the bloodstream or lymphatic system and travel to other parts of the body. There they start the process of forming a tumor all over again somewhere else (metastatic or secondary cancer).

Cancer treatment aims to remove tumors or limit their growth

There are many different types of cancer treatment. All of them aim to remove the malignant tumor, or at least limit how much the cancer can grow and spread. Some cancers can be removed by surgery. Medication (chemotherapy) or various types of radiotherapy are sometimes used to shrink tumors before surgery. These treatments might be used after surgery too, to destroy any cancer cells that are left and prevent the cancer from growing back (recurrence).

Chemotherapy and/or radiotherapy are still options even if the tumor can't be removed by surgery. The exact treatment will depend on various things, like the type of tumor and the stage of the disease. Medications known as cytostatic drugs are typically used in chemotherapy. These drugs can kill cancer cells or make sure that they don't continue to grow. Other medications prevent the development of new blood vessels that feed the tumor. That can slow the growth of the tumor. Some drugs interfere with the cancer growth process by reducing the effect of hormones and other chemical messengers on the cells. Nowadays there are also medications that can boost the immune system's ability to fight off certain types of cancer cells. Researchers are always looking for new ways to limit the growth and spread of cancer cells.