Center for Asbestos Safety

What Is Cancer?

The human body comprises of living cells numbering several hundreds of millions. Normal cells in the body grow, divide and die in a systematic manner. Throughout the early years of an individual’s life, normal cells in the body divide at a faster rate to facilitate physical growth. During adulthood, cell division takes place only to replace depleted or dying cells or to repair cells damaged due to injury.

Cancer starts when cells in a specific part of the body begin to grow in an uncontrolled manner. There are several different types of cancer, but all of them begin with uncontrolled growth of abnormal cells.

Growth of cancer cells is different from growth of normal cells. These cells don’t die, and instead continue to grow and produce new, abnormal cells. Cancerous cells can also spread to (grow into) other types of tissues, something that healthy cells cannot do. Uncontrolled growth and the ability to invade other types of tissues are some of the key characteristics of a cancer cell.

Cancer cells are formed due to damage to DNA, which is present in all cells and is responsible for all its actions. When the DNA in a normal cell gets damaged, it is either repaired by that cell or the cell dies. The damaged DNA in cancer cells does not get repaired and the cell itself does not die as it is supposed to do. Instead, the cancer cells continue to make new cells that are not required by the body. The new cells thus formed have the same type of damaged DNA as the cancer cells.

Individuals can inherit damaged DNA, but in most cases, the damage to DNA is caused due to errors that occur during the reproduction of normal cells or by specific substances present in the environment. In some cases, the probable cause of damage to DNA is obvious, for instance cigarette smoking. However, in most cases it is difficult to ascertain the cause.

In majority of cases, cancer cells lead to the formation of tumor. Certain types of cancers such as leukemia seldom form tumors. In such cases, cancer cells can be found in the blood and blood-forming organs, and these circulate via other tissues and grow there.

Cancer cells usually spread to other areas and organs of the body. Here, they start to grow and develop tumors that replace healthy tissue. This process is known as metastasis. It occurs when the cancer cells enter the bloodstream or the lymph vessels in our body.

Irrespective of where the cancer may have spread, its name is always derived on the basis of the cancer’s origin. For instance, even if breast cancer has spread to the liver, it will still be called breast cancer. Similarly, prostate cancer that has spread to the bone is called metastatic prostate cancer and not bone cancer. If mesothelioma starts in the pleura; it is called pleural mesothelioma. Cancer that starts in the peritoneal cavity is peritoneal mesothelioma, regardless or where it metastasizes to.

How different kinds of cancer behave varies significantly. For instance, breast cancer and lung cancer are significantly different diseases. They grow at varying rates and their response to treatment is different. Because of this, individuals diagnosed with cancer need specialized treatment, as relevant and appropriate to their specific type of cancer.

Each and every tumor is not cancerous. Tumors which are not cancerous are known as benign. These can create problems because they can grow significantly large and press on healthy tissues and organs. However, they cannot spread to (invade) other tissues. Since they cannot invade, it is also not possible for them to spread to other areas and organs of the body (metastasize). In most cases, these tumors are not life threatening.

Next: Symptoms of cancer

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