Tumor: This is an abnormal mass of tissue resulting from uncontrolled division of cells. It can be benign (non-cancerous) or malignant (cancerous).
Metastasis: This refers to when cancer cells break away from their original location and spread to other parts of the body via blood or lymph systems.
Oncogene: This is a gene that has potential to cause cancer. In normal conditions it helps regulate cell growth but when mutated or expressed at high levels it can help turn a normal cell into a cancerous one.