A cancerous growth “often called a malignant tumor” is composed of millions or billions of cells. Cells whether cancerous or normal are very small, so small that individually they can’t be seen by the naked eye, they are only visible under the microscope which enlarges the cells 50 to 100 times.
To give an idea, if we mince a cancerous tumor of the size of a finger tip so that the individual cells can be counted, such a tumor contains about one billion cancer cells. Each one of those cells if given the right environment can grow to form a tumor as large as the size of a football.
Unlike normal cells, cancerous cells continue to grow unchecked. When we cut our skin, the surrounding healthy skin tissue gets instantly stimulated to grow, those normal skin cells surrounding the cut divide forming new cells to cover the gap created by the cut. Once the gap is closed by the regenerating new cells, the process stops, because the normal cells obey the rules of checks and balances that control our body cells. To be precise, the normal cells have normal genes that obediently listen to the normal signals they get from the rest of the body.
For example, cells in the growing embryo continue to grow until puberty. After that signals go to the cells commanding them to stop growing at the size determined by the genetic makeup of that individual. That genetic makeup is inherited from the parents. That is why we look like our parents.
Various organs grow at different rates, again depending on the genetic makeup. A tall person has inherited genes from the parents that determine how long his or her bones are supposed to be. Likewise there are genes that determine the color of the skin and hair. Genes on the X and Y chromosomes determine if the growing embryo is going to be a girl or a boy.
All cells in our body have exactly the same genes on the 46 pairs of chromosomes, that is to say that each of the billions of cells in our human body has those same 46 pairs of chromosomes. But some genes become dormant in some body organ cells while others are active. For example, when we cut part of the liver it will regenerate, because the gene that controls regeneration stays active in the liver cells. The same can be said about the skin and the bones. However, if we remove part of the brain or damage it by a stroke, the brain cells do not regenerate. The brain cells, although they have the same genes of the skin and the liver, are inactivated permanently as soon as the brain is fully grown.
Cancer cells on the other hand are mavericks. They have lost the genes that make normal cells obey the rule of law that controls their growth and division. The reason for this is mutation. In normal cells there are genes called tumor suppressor genes, their function is to command the normal cell to stop dividing when the need arises. Cancer cells have lost those suppressor genes, so they continue to divide irrespective of the constant signals that they get telling them to stop doing so.
So what makes normal cells turn cancerous? As we said through mutation or call it damage of the tumor suppressor genes. Gene mutation is simply a minor change in the chemical structure of the gene. A gene is composed of thousands of chemicals; any trivial change in any of those chemicals can make the gene useless as if nonexistent. This mutation happens only when cells are dividing. During cell division the genetic makeup (chromosomes which are the collection of genes) are copied, so every cell becomes two, and when they divide again they become four and so on. Mistakes do happen during this process of DNA replication “DNA is the chemical name of the genes”. These mistakes can be random, because copying billions of molecules in an exact order is bound to create errors. Many of these mistakes result in cell death because the mutation can be so drastic that the cell can’t function normally. Normal cells have the mismatch repair genes; their function is to repair those errors.
Many cancers start because cells lose the mismatch repair gene function through mutations. Each cell has a pair of the mismatch repair genes, one on each chromosome. One mismatch repair gene is enough for the cell to stay normal. A cell has to lose both through two separate mutations to become cancerous. Some people are born with one mismatch repair gene missing or mutated. Such people need only one mutation in a cell for it to become cancerous. It is important to realize that it takes only one cell to lose both genes for cancer to be born.
When the cell turns cancerous, it acquires the survival advantage, since its division and multiplication becomes eternal and goes unchecked. Cancer cells become almost immortal; moreover they successfully compete with the surrounding normal cells growing at their expense. They are fit and represent a miniature of Darwin’s theory of survival of the fittest.
Darwin proposed some species acquired competitive characteristics that made them survive, whereas those who lacked crucial characteristics vanished. He called that evolution through survival of the fittest. He hypothesized that more than a century ago, a time when no one knew what genes are. The entire DNA was discovered a half century ago.