There is considerable evidence that tumor cells are often embolic in blood or lymphatic vessels without production of metastasis.Many tumor cells must be lost along the course.

• 许多研究表明：癌栓常出现与于血管或淋巴管内而转移并无发生，因为在此过程中，许多肿瘤细胞已被机体杀灭，从而无法完成转移的整个过程。