What is cancer?

Key points:

  • Cancer is caused by changes to DNA.
  • DNA contains the blueprint for life and is housed in the nucleus of almost all of the trillions of cells that make up the body.
  • This DNA instruction set tightly regulates cell division, growth and death.
  • DNA changes in two ways – via copying errors and environmental damage.
  • Everyone of us has the potential to develop cancer
  • Good changes have over millions of years allowed our species to evolve – think Darwin.  Bad changes can allow cells to get out of control and lead to cancer.
  • It’s not every DNA change that leads to cancer – rather particular mechanisms that regulate specific parts of the body have to be changed.  Only when the changes fit a particular pattern will cancer take hold.

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Cancer is caused by damage to DNA

What Is Cancer?

To help yourself with cancer, you need to understand what is cancer. This is no mean feat as cancer is complicated. Why? Because cancer is a genetic disease involving DNA mutation. It is uncontrolled cell growth that is unleashed by mistakes in our DNA. In normal cells, DNA carefully regulates cell life, growth and death. In cancer, these controls no longer work allowing cancerous cells to grow unchecked and ultimately spread to other parts of the body.

As humans, we try to protect ourselves and live as long as possible. We look for things that can harm us and avoid them. Cancer is similar – it follows a Darwinian path of survival. Cancer too seeks immortality by avoiding the body’s checks and balances – the irony is that cancer’s success is really a failure as unchecked growth ultimately leads to its own death.

To understand what cancer is, you first have to understand what cells are, how genes work and what epigenetics is. From that basis, it is possible to go on and form a model of how cancer starts, grows and spreads around the body. We can look at the different bodily processes it hijacks to allow this to happen. These are known as pathways and although at first sight they can seem very complicated, they are understandable at a basic working level. These pathways are also known as the hallmarks of cancer.

When you understand these cancer pathways you will have a better understanding how certain treatments, drugs particularly, work as they tend to target / interrupt one or more of these pathways. This pathway framework is also useful for understanding how other interventions, such as diet, exercise and stress reduction, are thought to act against or even reverse cancer’s advance. We say “thought” because in many situations it is not fully understood how a drug or lifestyle intervention works. Our knowledge of cancer is limited and the precise mechanisms of action are very complex and often unknown. explains what cancer is using a model

We will not go into these pathways in depth in this article, though we do outline them in detail in our video course, where we introduce and explain a Six Pathways Model of Cancer designed to help you better understand the disease.

What are cells?

The body is made entirely of cells – some 38 trillion of them – most of which are constantly renewing themselves. Cells die and are replaced – they are renewed by new cells just to keep the body running. In addition to this regular renewal of existing cells, the body undergoes particular cell growth in certain circumstances, such as when a child is growing or when a wound is healing.

Different tissues and parts of the body are made up of different specialized cells. Thus bone and muscle cells are different from blood cells, which are different from brain cells, and so on. What cells become (bone, blood etc.) and how they behave is all regulated by the body’s DNA. Cancer takes hold when DNA is damaged.

What Is The Primary Function of DNA?

DNA, also known as deoxyribonucleic acid, is the body’s blueprint; it’s the set of instructions that sustains life by telling cells what to do and when. It has evolved and changed over millions of years, and it’s this process of evolution that has allowed our species to become dominant. Around 100,000 years ago, our ancestors were middle of the food chain; not smart enough to outwit those with greater strength or speed. That changed as our DNA and brains developed. Unfortunately, this ability to change is a double-edged sword – it leads to survival advantages over time, but can also lead to cancer.

Human DNA is organized into strands of chemicals called nucleotides, but don’t get caught up on the jargon. What nucleotides are is simply strands of different chemicals and they hang together like beads on a necklace. The strands are in turn called chromosomes and human DNA is organized into 23 pairs of chromosomes. These 23 pairs are arranged in the famous double helix shape discovered by Crick, Watson, Wilkins and Franklin in the 1950s.

“Is There More You Can Be Doing After Cancer Diagnosis

Cell Composition

A cell has three main parts to it – the outer layer, known as the cell membrane, the center part, called the nucleus, and a liquid like substance called the cytoplasm in-between. DNA is found in the nucleus. It is the coding in the DNA that governs how a cell behaves – whether it divides, moves, grows, dies etc. When this coding goes wrong, cancer can take hold.

The three main parts of a cell

DNA controls everything – you can think of it as a very detailed and complicated instruction manual. The sort of weighty tome that used to accompany desktop computers in the 80s.

DNA Damage

DNA is fragile and can be easily changed / damaged. There are two main ways in which this damage occurs, which can lead to cancer. The first is through copying errors. As noted, one of the things that DNA provides for is cell growth. This occurs through cell division – known as mitosis. When cells divide, the DNA is copied so that each new cell contains the all-important blueprint of life. Yet, this copying process is imperfect and errors are sometimes made, which leads to a slightly different set of instructions being encoded in the new cells. It is thought that around two thirds of the damage that leads to cancer is caused by these copying errors.

The second way DNA changes and leads to cancer is through damage from environmental factors. It’s from the things we eat, from the water we drink, from the air pollution around us, from the alcohol we drink, from the cigarettes we foolishly smoke, from the radiation occurring naturally in the environment and from numerous other sources. It’s also from viruses that attack our body from the inside over long periods of time. Hepatitis C, for example, is known to lead to liver cancer. Another example is human papillomavirus (HPV), which is the leading cause of cervical cancer.

These things are known as carcinogens – they damage DNA, which can, but are not certain to, lead to cancer. They increase the probability of cancer, but don’t guarantee cancer. The best example of this is all the many smokers who don’t get cancer (and all the non smokers who do). It’s about probabilities, rather than certainties.

The short point is that our body is constantly bombarded with environmental chemicals that change the structure of our DNA and cause cell dysregulation.

Sounds terrible right? It would be, except it is not normally a problem as our bodies have a number of protective mechanisms to deal with this environmental onslaught. For example, damaged cells can repair themselves, or, failing that, commit cell suicide (called apoptosis, a key protector against cancer). Normally the body has no problem in eliminating badly behaved cells and remaining cancer free. It’s only when these protective mechanisms fail that cancer takes hold.

Understand that the potential for cancer lies dormant in all of us

What do we mean by this? Well, it is that our bodies already contain genes that allow for uncontrolled cell growth – everyone has them, and therefore the potential for cancer. These cancer genes are called oncogenes, but are only problematic when they are damaged or over expressed. Equally, we have genes whose function it is to control cell and cancer tumor growth – these are called tumor suppressor genes, and cancer only becomes a problem when they are damaged or under expressed. Genes are given weird names: myc, neu, fos, ret and akt are known oncogenes and p53, vhl and apc are known tumor suppressor genes.

Lights on a dimmer - epigenetics

What do we mean by over and under expression? This takes us into the field of epigenetics, which is beyond the scope of this article (you can learn more about epigenetics in our video course)

The journey from normal cell to cancer cell takes time

It’s important to understand that cancer cells normally develops over long periods of time as cells diverge from their normal state. The changes that ultimately lead to cancer occur slowly, normally taking between 2 and 40 years to develop, cause problems and lead to a cancer diagnosis. The changes operate in a step like process.

Certain changes typically occur first allowing cells to grow when they shouldn’t. These cells aren’t yet cancerous; then additional DNA damage occurs that knocks out the body’s defenses against this growth – cells no longer obey signals to stop growing or commit suicide.

Further DNA damage allows cells to the body’s blood supply so that the growing cancer mass can nourish itself with nutrients and survive. Yet further genetic defects will allow the cells to move from the original cancer site to other parts of the body – this is known as metastases, and it is this final step, the one that is the real problem. More than 90% of cancer deaths result from metastases, and it is this ability to move around the body that distinguishes malignant from benign tumors.

Ultimately, it is thought that all cancer starts from a single cell that has, over time, suffered a combination of DNA changes that allow it to grow unchecked and avoid the body’s inbuilt safety mechanisms. Of the trillions in the body, it only takes one cancerous cell to ruin everything.


We should note that this is the predominant theory of cancer (DNA mutation). A second theory is that cancer is primarily a metabolic disease, with DNA damage ancillary to that. See, e.g., Coller, Is Cancer A Metabolic Disease? Am J Pathol. 2014 Jan;184(1):4-17
See, e.g., Pepper et al, Cancer Research Meets Evolutionary Biology, Evol Appl. 2009 Feb; 2(1): 62–70
It’s not any damage that causes cancer, but rather a specific pattern that provides cells with special abilities that allows them to grow unchecked, avoid the body’s defenses and, ultimately, spread to other sites
Tomasetti, Vogelstein, Variation in cancer risk among tissues can be explained by the number of stem cell divisions, Science 02 Jan 2015: Vol. 347, Issue 6217, pp. 78-81
See, e.g., cancer development

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