Five tid-bits about cancer taken from my NPLEX studying:
1) Cancer cells have to replicate thirty-times before they become clinically detectable.
2) People often die from cancer not from the tumor itself, but because of the tumors secrete chemicals that cause cachexia (aka wasting). Cachexia causes a patient to continuously lose weight and basically starve to death. Even with eating and lots of food, cachexia can't be reversed.
3) Normal cells are programmed to die when they get old or unhealthy. This self-suicide mechanism is called apoptosis. Cancer cells cause the apoptosis mechanism to fail, meaning that sick, cancerous cells can keep on living, even though they should have died/undergone apoptosis. Basically, cancer cells highjack the mechanisms that normally keep our cells in check!
4) Chemotherapy and radiation don't always work against cancer because these treatment options work to prevent growing cells from growing any further. Unfortunately, the majority of cancers do not actively grow (up to 90% of cells in some tumors don't divide). The cancers that respond best to chemo and radiation are those rapidly dividing cancers (e.g. leukemia (cancer of white blood cells)).
5) When a cancer spreads, it metastasizes. This means that cancer has entered either the blood or the lymphatic system, and now that it has entered a rapidly moving transport system, the cancerous cells are able to reach almost any part of the body. If a cancerous cell were to get lodged in a capillary in the lung, for instance, it can take this opportunity to 'set-up camp' and make a new home here. The cancer has gone from the breast tissue, for example, and has now spread to the lung.