Cancer is a class of diseases characterized by out-of-control cell
growth. There are over 100 different types of cancer, and each is classified by
the type of cell that is initially affected.
Cancer harms the body when damaged cells divide uncontrollably to
form lumps or masses of tissue called tumors (except in the case of leukemia
where cancer prohibits normal blood function by abnormal cell division in the
blood stream). Tumors can grow and interfere with the digestive, nervous, and
circulatory systems, and they can release hormones that alter body function.
Tumors that stay in one spot and demonstrate limited growth are generally
considered to be benign.
More dangerous, or malignant, tumors form when two things occur:
1. a cancerous cell manages
to move throughout the body using the blood or lymph systems, destroying
healthy tissue in a process called invasion
2. that cell manages to
divide and grow, making new blood vessels to feed itself in a process called
angiogenesis.
When a tumor successfully spreads to other parts of the body and
grows, invading and destroying other healthy tissues, it is said to have
metastasized. This process itself is called metastasis, and the result is a
serious condition that is very difficult to treat.
In 2007, cancer claimed the lives of about 7.6 million people in
the world. Physicians and researchers who specialize in the study, diagnosis,
treatment, and prevention of cancer are called oncologists.
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