Tumours and tissues: similar homeostatic systems?

The currently prevalent somatic mutation theory of carcinogenesis and metastases explicitly assumes that cancer is a cellular disease, i.e. a disease of the control of cell proliferation and/or cell differentiation. Accordingly, explanations should always be sought for at a gene and/or gene product level, regardless of the level of organization at which the phenomenon is observed. Such a reductionist approach characterized the century-old effort to find cancer cell singularities, absent in normal cells, without apparent success, however. More recently alternative views have been put forward, assuming that cancer is a tissue-based disease involving disturbed interactions within the tissue architecture. In this review, selected reports on normal tissue homeostasis and bone marrow contribution to both tumour cells and tumour stroma are reviewed. Regarding normal tissues, the existence of a complex homeostatic system actually involving the whole organism emerges. Regarding tumours, remarkable similarities with normal tissue activities are apparent, providing some evidence that tumours share many biological features and processes with normal tissues. The review supports the concept that cancer is a tissue-based disease and that its pathological nature may result from unbalanced/untimely activation of otherwise normal physiological processes.