We propose the hypothesis that around a main invading tumor, there are local metastases in the surrounding tissue/organ. They occur as a result of cancer cell migration through the interstitial matrix and we call them true local metastases. They are composed of individual or nested cells but are difficult to identify because of their nonspecific appearance, close location to the irregular surface of the main tumor and observer's inability to deduce a three dimensional structure from a few two-dimensional histological pictures. The propensity of neoplasms to locally metastasize may vary greatly among different types and stages of tumors. Better knowledge of a tumor's three dimensional spread may influence treatment strategy.
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