Physiologic Anticarcinogenesis: Effects of Stable Strontium on Metastatic Bone Disease

Metastatic inefficiency (1) presents a unique challenge for the investigation of local and systemic factors in physiologic anticarcinogenesis. It appears that a point has been reached whereby there is general agreement that the transfer of cancer cells from the primary tumor to secondary sites is a multi-step process (2) and likely also multifactorial since each step is affected by different factors (3,4). Purely mechanical factors seem to be insufficient to explain why 99.9% of circulating tumor cells are destroyed before they are able to produce a viable metastatic focus. Recent animal studies indicate that only specialized cancer cells are capable of initiating metastatic foci and that they are to a certain degree site specific (5). There is a need for further development of animal models, whereby experimental conditions are controlled, in order to explain the diversity of response to treatment (6).