Cancer cells, believe it or not, depend on the very same means of survival as normal cells do. They must produce energy and replicate. But it is the very efficient way they do this, without any control, that turns a rogue cell into a devastating tumour. They are vulnerable, however, and because of this, scientists have developed ways of cutting off the energy and replication machinery. This is what chemotherapy does.
Have you wondered why chemotherapy affects certain healthy parts of the body too? This is because the drugs used are designed to interfere with the way cells divide. Any cells in the body which divide very quickly will also be affected. This is why people undergoing chemotherapy often lose their hair. Other cells that could be affected in this way include skin cells, cells lining the gut, and cells in the bone marrow which are destined to become the infection-fighting cells. So people having chemo need to be careful to avoid coughs and colds.
Two points to end on: there is good evidence that using a 'cold' cap during chemo slows down the growth of normal hair follicle cells and prevents hair loss - ask the Chemo nurse about this. And advances in immunology (infection control in the body) are such that a very good drug given just after chemo can boost the good white blood cells in the bone marrow.
Any questions, please ask.