What are cancer cells?
Cancer cells differ from normal cells in the body in many ways. The differences range from the types, characteristics, growth potential, properties, and more.
A cell is the basic unit block of all living creatures. During your life, the normal body cells are frequently reproduced and replaced by processes called mitosis or meiosis. This process takes 30 minutes to 90 minutes depending on the process of cell formation. This is how our body cells live their life cycle in our body.
A normal parent cell divides to produce two daughter cells, which build new tissues and replace cells that have died because of age or damage. Healthy cells do not produce daughter cells when there is no need.
Cancer cells, however, continue to produce copies and exhibit uncontrolled growth. They start to multiply very rapidly and begin to invade and destroy neighboring tissues. This abnormal condition is called cancer or malignancy. These cancer cells do not die but continue to grow and proliferate rapidly.
While normal cells do not grow when there is no need, malignant cells don’t stop growing and keep on dividing.
These abnormally growing cells clump together and form a growth or tumor, except of course in blood cancer. When this growth exhibits characteristics of cancer, it is called a malignant growth or a malignant tumor that keeps growing.
Blood cancer (leukemia) does not form tumors. But, they make many abnormal blood cells that build up in the blood.
However, not all tumors are malignant. The non-cancerous or non-malignant tumors are called benign tumors. They do not grow rapidly like malignant tumors and they do not invade the neighboring tissues.
The rapidly growing cancer cells form their own blood vessels to get nutrition and feed voraciously on account of their abnormal rapid growth, depriving the rest of the body of nourishment. These rapidly growing cancer cells can also spread to neighboring tissues and to distant parts of the body. This is called metastasis.
Types and names
There are many types of cancer cells and most of the cancers are typically named after the types of cells they originate in. These various cancer cells do not behave in the same way.
- Carcinomas are cancers that arise in epithelial cells that line bodily cavities
- Sarcomas are cancers that arise in mesenchymal cells of connective tissue in bones, muscles, blood vessels, and other tissues.
- Leukemias, lymphomas, and myelomas are “blood-related cancers” that originate in the bone marrow (leukemias and myelomas) or the lymphoid tissues (lymphomas). They feed on the nutrients present in the bloodstream and the lymphatic fluid. They do not form tumors.
- Cancers of the brain and the central nervous system are derived from cells of the brain and spinal cord.
- Mesotheliomas originate in the mesothelium, which is the epithelium that lines the pleurae, peritoneum, and pericardium. These are the membranes that line the lungs, abdomen, and heart respectively.
How are cancer cells formed?
Cancer is caused by changes to the DNA of the normal cell. These DNA changes that make the cell cancerous occur in sections of DNA called genes. These genetic changes transform the genes of the normal cells to become oncogenes (mutated genes that have the potential to cause cancer).
A normal cell becomes a cancer cell when the genes responsible for cell division are damaged.
Carcinogenesis or oncogenesis is the process by which normal, healthy cells transform into cancer cells. It is caused by a mutation in the genetic material of normal cells, which totally changes the normal process of cellular proliferation and apoptosis.
Carcinogenesis involves a complex series of several mutations to occur in the specific genes before a normal cell transforms into a malignant cell through cellular DNA damage.
This causes rapid and uncontrolled division of cells in the body, which can lead to the formation of tumors, benign or malignant.
Malignant tumors invade the neighboring tissues and spread to distant regions of the body causing a threat to life.
Damage to DNA can be caused by environmental factors such as exposure to radiation, chemicals, and other sources.
Aging is another risk factor, which may predispose to the development of cancer through several mechanisms such as accumulation of mutations, alterations in homeostasis, and chromosome instability.
Oncoviruses are viruses that can cause certain types of cancer.
Cancer cells look different
Under a microscope, cancer cells may look vastly different from normal cells. They
- are of varying sizes – some are larger than normal cells, while others are smaller
- are often of abnormal shape
- often have a nucleus that looks abnormal
They ignore cell-to-cell signals
Normal cells are continuously sending chemical signals to each other all the time, which they obey. They stop growing when the signal tells them they have reached their limit and will cause damage if they grow any further. Normal cells stop dividing when they come into contact with similar cells through a mechanism known as contact inhibition.
In cancer cells, however, this signaling system is prevented from happening and there is no stopping their growth. Cancer cells do not exhibit contact inhibition
The regulatory signals, which control cellular growth or initiate apoptosis get short-circuited in cancer cells. This results in their rapid growth, which may lead to the formation of tumors.
Normal cells in the body naturally adhere together and stay in the right place so that the tissues and structures of the body form properly. This is called cell adhesion or ‘stickiness’.
Cancer cells can lose the cell adhesion molecules on their surface that keep normal cells in the right place. They can, therefore, break away from their neighboring tissues.
They don’t specialize
Healthy cells keep on maturing and become specialized so that they are able to carry out a specific function in the body. This process is called differentiation.
Cancer cells reproduce so fast that they don’t have a chance to mature. As a result, they do not mature and hence do not function properly. Due to their rapid proliferation, they frequently generate changes in chromosome content.
Cancer cells don’t undergo apoptosis
Normal cells can repair themselves if there is damage to their genetic structure. This is known as DNA repair. If the damage is severe, they even self-destruct. Scientists call this process apoptosis.
However, the faulty molecules in cancer cells cannot decide whether a cell should repair itself, and hence there is no repair of the fault. A protein called p53 is responsible for this process of deciding whether the cell should repair the faulty gene or if the cell should die. But, since the cancer cells have a faulty version of p53, they don’t repair the cell damage adequately.
They ignore the signals that tell them to self-destruct and do not undergo apoptosis. This makes the cancer cells immortal.
With this unrepaired damage, these malignant cells go into overdrive. They grow more rapidly, start spreading to other parts of the body, and become resistant to treatment.
Dormant cancer cells
Cancer cells often become dormant to evade an attack from our immune system. Dormancy occurs when the cancer cells stop proliferating but they still remain viable and harbor the potential.
Dormancy is a stage in cancer where the cells stop multiplying but stay alive in an inactive state. They wait for appropriate conditions such as chronic inflammation or certain environmental factors that will trigger their proliferation again.
Cancerous cells can lie dormant for years.
Summarizing the characteristics of cancer cells
- The cancer cells are always on a high drive for growth and proliferation with inbuilt growth signals. They do not need stimulation from external signals.
- They do not undergo apoptosis (cell death).
- They have a limitless potential to replicate and produce infinite downline generations.
- They are insensitive to antigrowth signals.
- Continuous and sustained angiogenesis is the process through which cancer cells form new blood vessels from pre-existing vessels to obtain their own nutrition and feed voraciously.
- Metastasis is the process by which cancer cells invade the neighboring tissues and can travel and lodge in distant parts of the body.
Do we all have cancer cells and cancer genes in our bodies?
No, all of us do not have cancer cells or cancer genes in our bodies. Our bodies are constantly producing new cells, some of which can become cancerous. Our body sometimes produces cells that may have DNA that is damaged, but that doesn’t necessarily mean they will become cancerous.
Most of the time, these cells with damaged DNA either repair themselves or undergo apoptosis (cell death). However, failing repair and death, the cell can potentially become cancerous.
Similarly, we do not carry cancer genes in our bodies. Cancers that run in certain families are not at all linked to the genes that we inherit from our parents. The changes in the genes that cause most cancers start in the normal cell during the person’s life due to some triggering risk factors.