The Disease Process of Cancer
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.