A
tumo(u)r occurs when damage to a
cell's
genes causes it to divide uncontrollably. Tumors fall into two major categories,
benign or
malignant.
Benign tumours will continue to grow, but will not spread round the rest of the body, examples include
cysts and
moles on the skin.
Malignant tumors will continue to grow, and
cells will break off and travel round the body in the
blood or
lymph, starting
secondary cancers or
metastases, if not destroyed or removed fast enough,
maligant tumors are extremely likely to be fatal.
Tumors are caused by a combination of factors which cause the
genes controlling
cell division to mutate. The most common are:
genetic predisposition,
carcinogenic chemicals, and
radiation such as
ultraviolet light or
X-rays.