Organ vascularity and metastatic frequency.

The "hemodynamic" or "mechanical" theory proposes that the frequency of metastases in different organs is primarily determined by the numbers of cancer cells delivered to them in their arterial blood. This theory has not yet been adequately tested in man because reproducible, noninvasive measurements of organ blood flow have only recently become available. Correlation between these data and the metastatic frequency in 10 organs, in groups of patients with primary cancers in 15 anatomic sites, has therefore been sought. No correlation was obtained between metastatic frequency and organ weights, blood volumes, blood volumes per gram, "transit times," or blood flow. However, correlations significant at the 4-8% level were obtained between organ blood flow per gram and metastatic frequency in 4 of 5 groups of primary cancers with initial venous drainage into the portal system, compared with 1 of 10 draining into the caval system. At present, no definitive explanation can be offered for the apparent compliance of one set of primary cancers with the "hemodynamic" theory of metastasis, but not the others.