[A reductionnist approach of cancer]

According to a reductionnist view, a malignant tumour emerges and evolves as a consequence of genetic damages that accumulate in a cell. These damages generate a major clone and a number of sub-clones. A dynamic equilibrium emerges between these sub-clones in a given environment. Upon a multiform selective pressure, a great heterogeneity can appear in the primary tumour, between the primary tumour and its metastases, and between metastases in diverse tissues. The ability to identify this heterogeneity in installed tumours, and the detection of tumour cells before the appearance of this intra-tumour complexity, are major challenges in current oncology.