In a healthy body, the trillions of cells it’s made of grow and
divide, as the body needs them to function daily. Healthy cells
have a specific life cycle, reproducing and dying off in a way that
is determined by the type of cell. New cells take the place of old
or damaged cells as they die. Cancer disrupts this process and
leads to abnormal growth in cells. It’s caused by changes or
mutations in DNA.
DNA exists in the individual genes of every cell. It has
instructions that tell the cell what functions to perform and how
to grow and divide. Mutations occur frequently in DNA, but usually
cells correct these mistakes. When a mistake is not corrected, a
cell can become cancerous.
Mutations can cause cells that should be replaced to survive
instead of die, and new cells to form when they’re not needed.
These extra cells can divide uncontrollably, causing growths called
tumors to form. Tumors can cause a variety of health problems,
depending on where they grow in the body.
But not all tumors are cancerous. Benign tumors are noncancerous
and do not spread to nearby tissues. Sometimes, they can grow large
and cause problems when they press against neighboring organs and
tissue. Malignant tumors are cancerous and can invade other parts
of the body.
Some cancer cells can also migrate through the bloodstream or
lymphatic system to distant areas of the body. This process is
called metastasis. Cancers that have metastasized are considered
more advanced than those that have not. Metastatic cancers tend to
be harder to treat and more fatal.