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:
- a cancerous cell manages to move throughout the body using the blood or lymph systems, destroying healthy tissue in a process called invasion
- 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.
What causes cancer?
Cancer is ultimately the result of cells that uncontrollably grow and do
not die. Normal cells in the body follow an orderly path of growth,
division, and death. Programmed cell death is
called apoptosis, and when this process breaks down, cancer begins to
form. Unlike regular cells, cancer cells do not experience programmatic
death and instead continue to grow and
divide. This leads to a mass of abnormal cells that grows out of
control.