Molecular basis of tumor progression: mechanisms of organ-specific tumor metastasis.

Tumor cell metastasis is an extremely complex process governed by many different classes of molecules with each class having a separate function. Metastasis is the result of multiple sequential steps and is a highly organized, nonrandom, and organ-selective process. Recent advances in tumor and molecular biology have permitted the identification of a variety of heterogeneous molecules governing invasion (degradative enzymes, motility factors), adhesion (integrins, selectins, cadherins, immunoglobulin-like superfamily, annexins), and growth (paracrine and autocrine growth factors) of tumor cells. This diverse group of biological molecules is collectively responsible for determining whether tumor cells can progress from a single malignant cell to a lethal, multiorgan, metastatic disease.