Cell and tissue interactions in carcinogenesis and metastasis and their clinical significance.

This review describes a new vision for future directions in the study of metastatic cancer biology and pathology. It is based upon clinical and experimental observations on the constituent cell lineages within a neoplasm and on tumour-host interactions. The vision incorporates information from studies in population biology, developmental biology and experimental pathology as well as investigations upon human malignant disease. The assembled information reveals that invasion and metastasis are supra-cellular manifestations of "emergent behavior" among combinations of normal and malignant cell lineages in vivo. Emergent behavior is a combinatorial interactive process in which a population displays new traits which cannot be achieved by individuals acting separately and which subside when the specific population mix disaggregates. Disruption of such pathological interactions in the field of a developing primary or secondary tumour is, therefore, required to disable the malignant population and arrest progression without tissue destruction. These conclusions originate, in part, from principles which govern the sociobiology and group behavior of bees, ants, fish, birds and human societies. In all these social organisms, external factors can disrupt signaling mechanisms and induce expanding self-perpetuating rogue behavior, leading to social disintegration. These principles also apply to cellular societies composing higher animals, which likewise need intrinsic rules to maintain social order and avoid anarchy, and recognition of this is essential for advancing future research on the mechanisms involved in carcinogenesis and metastasis. Summarised evidence is presented here to support the conclusion that miscommunications between cells and tissues in the region of the developing tumour and its metastases are the main direct perpetrators of malignant disease. Genetic lesions (mutations, deletions, translocations, reduplications, etc.), commonly seen in cancers, can significantly disrupt important molecular pathways in the networks of communications needed to sustain orderly tissue/organ structure and function. However, genetic lesions can also, themselves, be induced by abnormal cell interactions initiated by extrinsic carcinogenic agents such as chemicals, viruses, hormones and radiation. The evidence shows that, irrespective of the initiating cause, it is this miscommunication in the region of a developing tumour and its metastases that is ultimately responsible for the emergence and progression of the disease. The article describes how this information collectively, provides a framework for designing specific novel therapeutic approaches targeting the cell and tissue interactions driving tumour metastasis and its manifold effects on the whole body.