Because cancer cells are made from normal cells through genetic mutation, because of this, the biggest difference between cancer cells and normal cells is that cancer cells have the three characteristics of infinite growth, metastasis and transformation, so cancer cells cannot be killed. 1. Infinite growth: due to the loss of adhesion of surface glycoproteins, cancer cells lose the ability of contact inhibition, while the continuous production of telomerase leads to the end of gene fragments not to be shortened with the number of generations of replication, so as to have the ability of infinite division, resulting in infinite growth of cells, which become immortal cells. 2. Metastasis: metastasis of cancer cells means that cancer cells can reach all parts of the body from the primary site, through lymphatic channels, blood channels or body cavities to continue to grow. As a result, cancer cells are found in every part of the body, which is incurable. 3. Transformation: Cancer cells can be transformed from one kind of cancer cells to another kind of cancer cells, which makes the originally effective drugs become ineffective.