Monday 1 November, 2021

What Is Cancer And How Does It Occur?

Dudi Warsito, PhD in Oncology, is a medical writer and researcher at cancer.se.

Dudi Warsito, PhD in Onocology and medical writer at cancer.se, is, in partnership with War On Cancer, sharing some key elements to know about cancer and science. What is cancer and how does it occur?

What we’ll cover in this article:
What is cancer?
Cell division
Tumors
The difference between cancer cells and normal cells
How does cancer occur?
Three types of genetic mutations
Invasion and metastatis
Blood cancer – cancer without a tumor

What is cancer?

Cancer is a group of diseases that are characterized by the cells in the body having lost their ability to control cell division. They grow and divide uncontrollably and eventually form a clump of cells – a tumor. In advanced cancer, individual cells from the tumor can break away and spread to other parts of the body and form metastatic tumors. Of the body’s over 30 billion cells, cancer can start from almost any cell.

The word cancer comes from the Greek word “karkinos”, which means crab. Here’s all about the origin of the word cancer.

Cell division

When new cells are formed 

Healthy, normal cells divide only when needed. External signals from nearby cells or tissue tell the cells when to divide and when to stop dividing. For example, it can happen when old or damaged cells need to be replaced with new ones, or when a wound needs healing. Cell division is a tightly regulated process that consists of several steps. At each step, there are so-called checkpoints – failsafes – which ensure that everything goes as it should. All components present in a cell, including the genome, must be copied and transferred to the new cell. 

It’s not uncommon for errors to occur in, for example, genetic changes (mutations), when the genome is copied. When errors occur, cell division is paused so that faults can be rectified by an internal repair system. When the repair is complete, the cell continues to divide. The cells that cannot be repaired undergo apoptosis, or programmed cell death, which is a kind of cellular suicide. This death of a cell benefits the organism as a whole as it prevents defective cells from continuing to divide and turning into cancer cells. 

When cell division goes wrong

Despite strict regulation and all the failsafes that exist in the development of new cells, cell division can go wrong. For example, the repair system may not work properly or cell division may not be paused. In these cases, damaged and defective cells are then allowed to grow and divide when they are not normally able to do so. Cells that divide uncontrollably eventually form a lump called a tumor. There are two types of tumors, benign tumor and malignant tumor, the latter is cancerous.

Tumors

Benign tumor

It’s important to remember that not all tumors are dangerous. For example, a harmless lump of fat can form. These are called benign tumors. A benign tumor can’t grow into other tissues or spread to other organs. Benign tumors can be removed if desired or needed and rarely return.

Malignant tumor

A malignant tumor consists of cells that have changes in the DNA that allow them to grow uncontrollably. Malignant tumors can become so large that they grow in and crowd out surrounding tissue and organs. Cells from the tumor can spread and form new tumors (metastases) in other tissues and organs. Malignant tumors are classified as cancer.

The difference between cancer cells and normal cells

Cancer cells differentiate themselves from normal cells in several ways. 

Have no need for external signals

Cancer cells do not need external signals to tell them to divide – they do so anyway. Normal cells, on the other hand, need external signals that tell them when to divide and when not to.

Ignore stop signals

Cancer cells ignore stop signals that tell them to stop cell division or die through apoptosis.

Grow into surrounding tissues and organs

Cancer cells can grow in and crowd out nearby tissue and organs, as well as spread to other parts of the body. Healthy, normal cells stop growing when they encounter other cells, which is called contact inhibition.

Promote blood vessel formation

Tumors have a great need for oxygen and nutrients to be able to grow. Tumor cells send signals that tell the body to form new blood vessels, also called angiogenesis, which transports oxygen and nutrients in the blood to the tumor. Angiogenesis is one of the most important hallmarks of cancer.

Manipulate the immune system

An important feature of cancer cells is their ability to manipulate and hide from the immune system. Cancer cells can send signals telling the immune system telling it to protect them instead of attacking them.

Several genetic changes 

Cancer is formed when normal cells accumulate many genetic changes, so-called mutations. Mutations aren’t uncommon but in most cases, the cell can repair them. Cells that cannot repair the mutations are eventually transformed into cancer cells.

How does cancer occur?

Cancer is a genetic disease that occurs due to changes in genes that regulate cell function, especially those that regulate cell growth and cell division. Cancer is a complex disease not only because there is a great deal of variation in which genes are altered between cancer forms, but also variation within each cancer form. 

Mutations can occur by missing failsafes during cell division or by environmental factors such as the sun’s ultraviolet rays and tobacco smoke. It’s also possible to inherit mutated genes from your parents. In most cases, the body is good at repairing mutations or getting rid of defective cells before they become cancer cells. However, this ability deteriorates as we get older, which is why cancer is considered an age-related disease, as the risk of becoming ill increases with age.

Develops in several steps

In order to develop cancer, there needs to have been an accumulation of several mutations over a longer period of time. For example, inheriting a mutated gene does not mean that you will be diagnosed with cancer – it only means that you have an increased risk. For every mutation that occurs in a cell, the worse it functions. After accumulating several mutations, the cell is so broken that it loses the ability to control its cell division and begins to divide uncontrollably.

Genes that increase the risk of cancer

Mutations can occur in all genes, but there are three main types of genes that are linked to cancer. The common denominator in these three gene types is that they promote uncontrolled cell division when mutated.

Three types of genetic mutations

  • Oncogenes
  • Tumor suppressor genes
  • DNA repair genes
Oncogenes

Oncogenes are genes that are involved in the growth and division of normal cells. They are especially active in cells that divide quickly and often, and in, for instance, wound healing when new cells must be formed to replace damaged cells and heal the wound. When oncogenes are mutated, they become overactive and promote cell division even when not needed.

Tumor suppressor genes

Tumor suppressor genes are the opposite of oncogenes – they slow down cell division. When the DNA is damaged, they make sure to pause cell division so that the damage can be repaired. A tumor suppressor gene that is mutated loses its braking function and results in the cell dividing uncontrollably.

DNA repair genes

As the name suggests, DNA repair genes repair errors in the DNA that can occur  when the genome is copied or if exposed to a lot of UV radiation. Cells with changes in DNA repair genes accumulate mutations that cannot be repaired in other genes. This, in turn, can result in a normal cell being transformed into a cancer cell.

Invasion and metastasis

A characteristic of malignant tumors is that they can penetrate into the surrounding tissue and organs in a process called invasion. The cells in the tumor secrete enzymes, so-called proteases, which act as molecular scissors. Proteases break down the barrier that exists between the tumor and surrounding tissue and organs. The tumor can get past the barrier and crowd out tissues and organs.

Metastasis and metastases

In advanced cancer, individual tumor cells spread to other parts of the body (metastasis) and form new tumors (metastases). Metastases are the primary cause of ineffective treatment of cancer and death. In order for the cells to spread and form new tumors, they need to break away from the primary tumor. After doing so, they go through a difficult and challenging journey through the body to reach their new place. Only a small percentage of those cells survive.

Just like in an invasion, the tumor cells secrete proteases that cut off the connections that hold the cells together in the tumor. The free cells can then travel to nearby lymph nodes to travel with the lymphatic system or blood system to get to other parts of the body. The few cells that survive the journey may eventually begin to grow and divide again, forming metastases.

Metastases are difficult to treat because they spread throughout the body, and can be hidden and difficult to find. As cancer cells spread, they acquire additional genetic changes that make them drug-resistant (as of today). Drugs that were initially effective may lose their ability to attack the cancer if it has advanced.

Blood cancer – cancer without a tumor

Most cancers start in the form of a tumor. However, blood cancer is a group of cancers that do not develop tumors. There are three forms of blood cancer: leukemia, myeloma, and lymphoma. Each form consists of even more forms of blood cancer.

In leukemia, the blood cells suffer from genetic changes and then move freely throughout the body via the blood system. Myeloma occurs in the white blood cells of the bone marrow. White blood cells form antibodies against viruses and bacteria, and are part of the immune system. Lymphoma is a group of cancers that originate in the lymphatic system.

The properties of cancer cells in blood cancer are the same as in cancers that start with a tumor. For example, they have the characteristic of dividing uncontrollably and no longer die according to the programmed schedule.

Dudi Warsito, PhD in Oncology, is a medical writer and researcher at cancer.se.

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