The Mechanism of Cancer Metastasis 【http://www.pathology.fun/ | 病理学教研室】
Metastasis is the spread of cancer from a primary tumor to distant sites of the body and is a defining feature of cancer. Three steps, as follows, are necessary for production of metastasis: (1) Invasion of cancer cells into lymphatic or blood vessels or into appropriate tissue spaces. (2) Detachment of the cells with immobilization or other mechanical transport, and (3) lodgment and progressive growth of the cells in a new location. Every cancer has its own particular growth characteristics, including the ability to invade and metastasize, the time required for metastasis, and the place to which metastases occur. Metastatic ability of a tumor is, of course, influenced by its location, since the nature of the vascular supply of the primary site is important. Many cancers cell seem to be capable of entering the step in the development of metastasis without necessarily continuing the process to the point of completion. For example, blood vessel invasion is relatively common in many cancers, but it does not necessarily mean that metastasis has already taken place, or that it will. Transport, the second step in the development of metastasis, is more or less mechanical. It is assisted by natural movements of the part, such as peristalsis and by excessive manipulation of the tumor by the patient or physician. Again, however even the presence of tumor cells in the blood stream does not necessarily mean that metastasis will take place. There is considerable evidence that tumor cells are often embolic in blood or lymphatic vessels without production of meta
转移是恶性肿瘤的重要特征，也是恶性肿瘤从原发部位蔓延到机体远处的组织的必要步骤。恶性肿瘤的转移有以下三个必要步骤：1.恶性肿瘤细胞侵袭淋巴道、血道或相应的组织部位。2.扩散的恶性肿瘤细胞以癌栓或其他方式转运。3.转移的恶性肿瘤在新的部位留居并持续生长。各种恶性肿瘤细胞各具生长特性，包括：侵袭和转移能力，转移所需的时间及好发部位。因为恶性肿瘤原发部位的血供十分重要，所以恶性肿瘤转移能力理所当然地受其影响，许多恶性肿瘤似乎都具备进入转移过程首发步骤的能力，而未能完成整个过程，例如：血道侵袭常见于许多恶性肿瘤，但这并不意味转移已经或将要发生。转运是整个转移过程的次行步骤，受不同程度的机械性因素，如：引起对恶性肿瘤组织触动的行为，例如器官的蠕动以及病人或医生对肿瘤的不适当处理等，均可能导致肿瘤细胞的扩散转运。然而，即使在血道中发现了肿瘤细胞，也并不意味转移已经完成。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。
It is evident that the third step in the development of metastasis is of much importance, tumor cells must lodge and grow in their new location. Not all organs and tissues are equally susceptible to the development of metastases. For example, metastases are relatively uncommon in the spleen or in skeletal muscle, although both most receive many tumor emboli. Conversely, metastases grow well in the liver. Such difference in the "soil" are not well understood and may be related to such factors as variation in vascular size and permeability, local nourishment and local resistance.
显然，在转移过程中的第三个步骤，即：发生转移的肿瘤细胞必须在新的组织器官留居和生长十分重要。而且，并非所有的组织或器官都具有适合转移的肿瘤细胞留居和生长的条件，例如：在脾脏或骨骼肌中就罕见转移瘤，虽然两者必然大量存在着接受转移的肿瘤细胞的机会。相反，转移的肿瘤细胞在肝脏往往生长良好，这种类似于“土壤” 性质差别的具体机制尚未被阐明，可能与血管的腔径，肿瘤细胞对血管的侵袭能力，组织或器官局部的营养状况，以及机体的抵抗能力等因素有关。
