Malignant neoplasms are capable of metastasizing. A metastasis represents a malignant neoplasm that has traveled from its primary site of origin to a distant site. This is an example of metastases to the liver. Note that the tan-white masses are multiple and irregularly sized. Like many large metastatic lesions, there is central necrosis.
A primary neoplasm is more likely to appear within an organ as a solitary mass. The presence of metastases is an indication that a neoplasm is malignant. The original clone of cells that developed into a neoplasm may not have had the ability to metastasize, but continued proliferation of the neoplastic cells and acquisition of more genetic mutations within the neoplastic cells can give them the ability to metastasize.