Several hundred oncogenes - genes which which have to potential to increase the risk of cancer - have now been identified. The way(s) in which they do so is as yet unknown.
A fundamental aim of cancer research is to identify the molecular changes that cause normal cells to evolve into malignant tumors. Malignant transformation has been proposed to occur as a consequence of the accumulation of genomic aberrations that successively overcome the cellular barriers to malignancy. Although a concerted effort has been made to discover the complement of molecular aberrations required for malignant transformation, the spectrum of events that must occur in a single cell, including which oncogene activation and tumor suppressor gene inactivation events can cooperate to induce malignant transformation, has remained elusive."
See: Are oncogenes sufficient to cause human cancer? in PNAS November, 2010.