Cancer 102: How It Grows and Spreads

Previous entry talks about how a cancer starts. If only the cancer would stay in place, then it won't be difficult to treat with surgery. Unfortunately, the way most cancers grow and spread complicates things a bit.

Specific cancers may have different preferences, but in general the characteristics of cancer growth and spread are:

• Initiation: the transformation process of a normal cell into a cancer cell, from the first mutation until it escapes the body's defense mechanism. 
• Proliferation: the process in which the rate of cell growth of the cancer cells overcome the rate of cell death. Hormones and growth factors plays important role in affecting the rate of growth of certain cancers. Even though cancer cells are dubbed immortal, they do die because the body's immune system is constantly at work and because they grow so fast, from lack of nutrients. It is believed that the cancer cells achieve their proliferation through the initiation of stem cells which are normally abundant in actively growing tissues, such as in tissue repair.
• Invasion: the process in which the cancer cells overcome the natural boundaries of different types of tissues in our body. Invasion is one of the hallmark characteristics of a malignant tumor. Normally different types of tissues have very well defined borders. You won’t find skin cells growing in deep muscle, or liver cells growing in the stomach.
• Angiogenesis: the formation of new blood vessels to provide nutrients for the growing cancer cells. Tumors could only reach a certain size before they would exhaust themselves of nutrients if it were not for angiogenesis. In other words, this is the process where a cancer steals the body's resources to feed itself.
• Metastases: is the ability of cancer cells to spread to different parts of the body via the bloodstream or the lymphatic system. Metastases is another hallmark of malignant tumors. 

Every stage of development mentioned above can be interfered by different types of cancer treatment such as radiation or chemotherapy. Cancers that are growing rapidly and prone to metastases are more likely to be affected by these treatments compared to slow growing cancers which may yield better result with surgery. 

Cancer 101: How It Starts

Being immortal is not always a good thing. Take cancer cells, for example.

A normal cell carries genes inside its nucleus. These genes carries information that controls the cell's behavior including when it will grow and when it will die. Normally if something goes wrong within the cell, it is programmed to die. However, sometimes this fail-safe mechanism misses, allowing a cell to keep dividing uncontrollably until it forms a tumor.

Technically, every abnormal growth is called a tumor. It can be either benign or malignant. A benign tumor usually grows slowly or stop growing at one point and does not spread to other parts of the body. Cancer is a malignant tumor, which keeps growing and may spread to other places through the bloodstream or the lymphatic system.

The Mutation

Mutation is the start of a cancer.

Mutation means that a gene has been damaged or lost. Genes decide what kind of protein a cell will produce. Therefore, a mutated cell may produce too much or too little protein. Some proteins controls how a cell behaves. For example, when a hormone acts on a structural protein, it then sends a series of signals which tell the cell to reproduce by dividing into two.

Because of mutation, a signaling protein may be permanently switched on or proteins whose job is to control and limit cell division may be switched off. Often times, the cause of this mutation is a carcinogen. For example, there are carcinogens in cigarette smoke. Virus infection and ionizing radiation may also trigger these changes. Mutated genes can also be inherited.

The Genes

There are three different types of genes that plays important roles in cancer formation.

• Oncogenes are genes that encourage the cell to multiply. When people talk about cancer genes, this is what they usually meant.
• Tumor suppressor genes are the 'police' genes that stop the cell from multiplying. If one of these genes becomes damaged and stops working, then the cell will carry on dividing. In other words it becomes immortal, which is one of the properties of a cancer cell. The best known tumor suppressor gene is called p53.
• DNA repair genes repair other damaged genes. Mutations happen a lot more often than you may think. However, thanks to these repair genes, not every mutation will develop into cancer.

What happens after mutation?

It is not easy for a normal cell to turn into a cancer cell. Our body is equipped with means to prevent it from happening. Mutated cells often destroy themselves or the immune system might recognize them as abnormal and attack them. DNA repair genes are able to repair the mutations so that it takes more than a single mutation in order to start a cancer. It can take a long time before enough mutations happen for a cell to become cancerous. This is why most types of cancer are more common in older people.

The place where a cancer begins is called the primary cancer. Once developed, the cancer may spread locally into surrounding tissues. Cancer cells may also break away from the primary cancer and be carried off in the blood or lymphatic system, starting a new tumor in other parts of the body. A tumor that grow from from a cancer that have spread are called secondary cancer or 'metastases'.