Metastasis: a review of recent advances.

Abstract

Summary Recent developments in research on metastasis have been reviewed. The process of metastasis begins when cells of the primary cancer invade surrounding tissues. At least one major factor responsible for this invasion is decreased adhesiveness of cancer cells, a property associated with deficient calcium and macromolecular abnormalities on the cell surface. Because of decreased adhesiveness cancer cells can separate from each other, move into surrounding tissues, and penetrate vessels. Following vascular invasion, tumor cell emboli are discharged into the blood stream. Most of these emboli are arrested by the first capillary or arteriolar bed, but some emboli may immediately pass through the capillaries and be carried to other regions. The pattern of distribution of metastases depends in part on mechanical factors and, in part, on recently recognized effects of hormones, notably of the adrenal. These hormones act on the tumor embolus or on the tissue where it has lodged. Studies on the lymphatic spread of cancer reveal that tumor cell emboli of carcinomas are arrested in the subcapsular sinus of one or more lobules of the lymph node, and it is here that early growth occurs. The cancer is contained by the node for some time before spread to the next node occurs. While growing in a node, the cancer has no supply of lymphatic vessels. When tumor emboli reach the thoracic duct, some of them may go directly to nearby lymph nodes without first going through the lungs.

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