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According to the most widely accepted theory of cancer development,
cancer originates in a single cell somewhere in the body.
The cell divides and grows in the organ of origin, causing
a localized tumor. Cancer cells then spread to adjacent tissues
or regional lymph node drainage areas, and then advance to
distant organs or structures, creating metastatic tumors.
Cancer can spread directly from the organ of origin through
the bloodstream into distant organs without involving adjacent
organs and regional lymph nodes.
Many cancers go through a matured course, advancing in tumor
size or involvement to regional nodal involvement and eventually
to distant metastasis. Small tumors can metastasize, with
the first sign of the cancer being the metastasis.
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