Cancer is a disease characterized by the development of abnormal cells that keep dividing uncontrollably with the ability to colonize and destroy normal tissues in the body. For example, ovarian cancer, prostate cancer, malignant pleural mesothelioma (MPM) and some other type of cancers often have the ability to spread throughout the body. Many cancers form solid tumors, which are masses of tissue while others such as leukemias (cancers of the blood) generally do not form solid tumors.
Cancerous tumors are classified as
- malignant tumors, meaning they can spread into, or invade, nearby tissues in addition to the fact that as these tumors grow, some cancer cells can break off and travel (metastases) to distant places in the body through the blood or the lymph system and form new tumors far from the original tumor. Sometimes, malignant tumors grow back after surgical removal.
- benign tumors, meaning they do not spread into, or invade, nearby tissues. It is worth mentioning that benign tumors can sometimes be quite large. They usually do not grow back after surgery. However benign brain tumors can be life threatening.
Although cancer is classified as a second-leading cause of death worldwide, the increase of the survival rates is impressive for many types of cancer nowadays due to the improvements in cancer diagnosis and its treatment. Signs and symptoms of cancer vary depending on the affected part of the body. Within the cells, DNA is packaged into a wide number of individual genes containing a set of instructions directed to the cells and telling them what functions to perform, how to grow and divide. Errors in these instructions can result in the cell stopping its normal function and may allow a cell to become cancerous.
A gene mutation can instruct a healthy cell to grow and divide more rapidly. This creates many new cells having all that same mutation. However, normal cells know when to stop growing so as to keep the right number of each type of cell. Unlike normal cells, cancer cells lose the tumor suppressor genes (the controls that tell them when to stop growing). A mutation in a tumor suppressor gene allows cancer cells to continue growing and accumulating.
DNA repair genes look for errors in a cell's DNA and make required corrections where applicable. A mutation in a DNA repair gene can mean that other errors have not been corrected, leading cells to become cancerous. These mutations are the most common ones found in cancer even if many other gene mutations can contribute to causing cancer. That is why cancer is said to be caused by mutations (changes) to the DNA within cells.
Several reasons that can induce gene mutations include: Gene mutations inherited from parents accounting fortunately for a small percentage of cancers and are mostly encountered for example in breast cancer. Most gene mutations are induced (e.g. occur after birth or are not inherited) by external or environmental factors. Some of these factors are smoking, radiation (ionizing radiation in particular), viruses, carcinogens (cancer-causing chemicals), obesity, hormones, chronic inflammation and a lack of exercise.
