In the human body there are about 6 trillion cells. Even after losing some cells from injuries or metabolism, cellular divisions will create new cells that replace the exact number of the lost ones. However in the case of cancer cells, they repeat the division the by its own, destroying the body balance. Cancer cells also can transfer to other parts of the body by flowing into the blood and lymph.
In Kampo medical term, the human body is more prone to illnesses when True Qi is weak. In the case of cancer, the balance between Yin and Yang falls, and this incapacitates True Qi to remove Evil Qi. When Evil Qi is accumulated in the body without being removed by True Qi for a long time, it turns into toxin that causes Cancer. True Qi in the sense is a vitality for us to continue living. In other word, we can work on prevention of illnesses by maintaining True Qi in the body. In terms of treatment, Kampo medicine focuses to Tonify True Qi and Release evil Qi.