metastasis(redirected from Cancer of unknown primary)
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a secondary pathological focus arising from the transfer of a pathogenic principle (tumor cells, infectious agent) from the primary site of affection by the lymph or blood.
In the modern view, the term “metastasis” generally applies to the spread (dissemination) of malignant tumor cells; the spread of an infectious principle is usually described by the term “metastatic infectious focus.”
Benign tumors are also known to metastasize, and the capacity to do so is inherent in normal cells of various origin (in placental villi, adipose and hematopoietic bone-marrow cells). A distinctive feature of metastasizing tumor cells is the uncontrollable growth of the metastasis, relating it to primary foci of malignant growth. Metastatic tumor nodes retain other properties of primary tumors as well, such as microstructural features and the capacity to form the same products; however, metastatic nodes often have a more primitive structure and consist of functionally less mature cells than do the original tumors.
When tumor cells spread chiefly through the lymphatic vessels, metastases generally appear in the lymph nodes closest to the primary site. Although much research has been devoted to the routes and anatomical patterns of lymphogenous metastasis, the biological patterns of formation of lymphogenous metastases remain obscure. The mechanisms of hematogenous metastasis (to the lungs, liver, bones, and other viscera) are better understood. Four stages in the development of hematogenous metastasis are distinguished: (1) the detachment of cells from the primary tumor node and their penetration of the blood through the vascular wall; (2) the circulation of the tumor cells in the blood; (3) the attachment of the cells to the vascular wall and the start of intravascular growth; and (4) the rupture of the vascular wall by the tumorous masses and the subsequent growth of the metastasis into the tissue of the affected organ. The presence of metastasis indicates that a tumorous process has shifted from a local growth phase to a phase of generalization. A distinction is made between solitary metastasis, which generally can be removed surgically, and multiple metastases, which require combined treatment using radiation and chemotherapy.
N. S. KISELEVA