In order for a cell to become cancerous, oncogenes must be active and tumor suppressors inactive. Oncogenes are genes which carry genetic material capable of inducing cancer. Tumor suppressors, on the other hand, function as a sort of "anti oncogene." In other words, tumor suppressors work to stop uncontrolled cellular growth and prevent cells from becoming cancerous. So if oncogenes are active and tumor suppressors are inactive, then there is nothing to prevent the cell from growing cancerous.