Cancer is a group of
diseases in which
cells are aggressive (grow and
divide without respect to normal limits), invasive (invade and destroy adjacent tissues), and/or
metastatic (spread to other locations in the body). These three
malignant properties of cancers differentiate them from
benign tumors, which are self-limited in their growth and do not invade or metastasize (although some benign tumor types are capable of becoming malignant). Cancer may affect people at all ages, even
fetuses, but risk for the more common varieties tends to increase with age. Cancer causes about 13% of
all deaths. Apart from people, forms of cancer may affect animals and plants.
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Cancer that occurs in families more often than would be expected by chance. These cancers often occur at an early age, and may indicate the presence of a gene mutation that increases the risk of cancer. They may also be a sign of shared environmental or lifestyle factors.