Host and tumour factors in cancer metastasis.

The process of cancer metastasis is sequential and selective and contains stochastic elements. The growth of metastases represents the endpoint of many lethal events that only few tumour cells survive. Primary tumours contain cells with heterogeneous metastatic properties, and the outcome of metastasis depends on the interplay of tumour cells with various host factors. Collectively, then, our studies and most data reported by others have led us to conclude that metastasis is a highly selective process regulated by a number of mechanisms. This belief is contrary to the once widely accepted notion that neoplastic dissemination is the ultimate expression of cellular anarchy. In fact, suggesting that cancer metastasis is a selective process is a more optimistic view in terms of cancer therapy than the one that contends that tumour dissemination is an entirely random event. A selective biological process is regulated by the interaction of tumour cells with their host, and these complex interactions can be studied and manipulated. A better understanding of the complexity of the processes of tumour evolution, progression, and metastasis should lead to improvements in the treatment of cancer.