Patterns of tumor metastasis: organ selectivity in the spread of cancer cells.

More than a century ago, Fuchs recognized that although tumors varied in their propensity for metastasis, there was, as well, discrimination in the different organs of the body, some providing a more fertile soil for growth for specific tumors than others. Paget dramatized this clear distinction between the intrinsic properties of the cancer cell and the properties of the host when he expanded on the analogy between tumors and plants: "When a plant goes to seed, its seeds are carried in all directions; but they can only live and grow if they fall on congenial soil." Paget is almost apologetic as he contrasts the work of those that study the 'seed' to his own work on the 'soil': "The best work in the pathology of cancer is done by those who...are studying the nature of the seed. They are like scientific botanists; and he who turns over the records of cases of cancer is only a ploughman, but his observations of the properties of the soil may also be useful." In a time where the primary emphasis in cancer research is at the level of gene expression, of regulation and of epigenetic modification of the "seed," those individuals, such as Pauli and Lee, who study the properties of the host environment should not be ignored. Not only are the observations of the 'soil' useful, they provide essential information without which we will not be able to understand the nature of the metastatic process.