How do cells "know" what they're meant to do?

Cells become specialized in order to perform particular tasks. Some cells will come together to form skin or a finger, for example.

The DNA (genes) in the cells normally lets them "know" what they should do. In other words, which other cells to join up with and stick to – and also when to stop replicating and die. Each type of cell has a particular role and set of information or instructions in their DNA. That's how they know that fingers should only grow on hands, for instance.

The instructions are clear, and healthy cells follow them. An example: If we cut our finger, the skin cells will start replicating and make new skin to heal the wound. If we lose a fingernail, our cells can grow a new one. But the cells can't make an extra finger if we lose one.

The role of hormones, blood and the lymphatic system

Our hormones carry messages to our cells, triggering the cells to take action. These messengers are carried by our blood in our blood vessels. The blood carries other things that cells need, too – such as oxygen and glucose (sugar). 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. It is a part of our body’s defense system (immune system), and it drains away bacteria and germs.

Normal cells

Benign and malignant growth

Cells become abnormal if their DNA – which carries the instructions they need – becomes damaged. Then they look different, and they may also have different properties. If these kinds of abnormal cells grow in body tissue such as skin, it is referred to as dysplasia. As long as there are few abnormal cells and they're kept under control by our immune system, they won't harm us. Sometimes these kinds of cells go away on their own. But if they keep on changing and start to divide uncontrollably, forming lumps or growths, then one of the more than 200 diseases called cancer develops. Growths are generally called tumors.

The difference between malignant (cancerous) and benign (non-cancerous) tumors is 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. Some types of cancer grow very fast, and others grow very slowly and only start causing problems after many years. Particularly older people may have a slowly growing tumor that never causes noticeable symptoms in their lifetime.

Benign tumors usually don't cause much damage and aren't normally life-threatening. But there's no guarantee: Benign growths may sometimes become malignant after some time.

How do cancer cells behave?

When cancer cells replicate and divide, 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. This means that they might break away, move through the blood vessels or lymphatic system, and start growing somewhere else in the body. That is known as metastasis.

Carcinoma in situ

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

In order to grow, tumors start making their own blood vessels (angiogenesis). The blood vessels supply the tumor with extra oxygen, glucose (sugar) and hormones. As a result, the tumor can grow into surrounding tissue. It is then called invasive cancer.

Invasive 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).

What are the treatment options?

There are many different types of cancer treatment. Some cancers can be removed by surgery. In chemotherapy, medications are used with the aim of preventing cancer cells from dividing and growing uncontrollably. Radiotherapy (radiation therapy) destroys cancerous tissue with the help of high-energy rays.

Some medications prevent the development of new blood vessels that feed the tumor. Others interfere with cancer growth 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 certain types of cancer cells.

The most suitable treatment option will depend on various things, like the type of tumor and the stage of the disease. Researchers are always looking for new ways to limit the growth and spread of cancer cells.

Sources

• Brandes R, Lang F, Schmidt R. Physiologie des Menschen: mit Pathophysiologie. Berlin: Springer; 2019.
• Kasper DL, Fauci AS, Hauser SL et al. Harrison's Principles of Internal Medicine. New York: McGraw-Hill; 2015.
• Menche N. Biologie Anatomie Physiologie. München: Urban und Fischer; 2016.
• Pschyrembel Online. 2021.

• IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

  Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

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