| Cancer
isn't one disease, but a group of diseases, which cause cells
in the body to change and grow out of control. Most types of
cancer cells form a lump or mass called a tumour. Only a few
cancers don't form a tumour, such as blood cancers (leukemia).
Cells from
a tumour can break away and travel to other parts of the body
and,
from there, continue to grow. This spreading is called metastasis.
When cancer spreads - for instance, if breast cancer spreads to
the
lungs - it is still named after the part of the body where it originated.
In this case, it is still breast cancer, not lung cancer.
A cancerous tumour is called a malignant tumour. Tumours, however,
are not all cancerous. Tumours that are not cancerous are called
benign. In most cases, benign tumours are not life threatening,
and do not grow and spread the way cancer does.
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