This occurs when cancerous cells from a tumor enter the bloodstream and move to a new location. These new cancerous growths are known as metastases. Causes There are many different factors that can affect the cells and result in mutations that lead to cancer. These factors can be either external or internal. External External factors that trigger mutations and cancerous growths are known as agents.
Carcinogens are agents that are known to cause cancer.
One of the best known carcinogens is tobacco. Internal Cancer, or a susceptibility to cancer causing mutations, can also be inherited. Looking at a family's medical history can indicate an individual's risk of inheriting cancerous traits. Each year people are diagnosed with over 100 diseases that are classified as types of cancer. In 1999 alone over 1,200,000 people were affected by cancer, and it has been named the second leading cause of death in the United States.