But a cancer cell doesn't obey the rules. The change in its genetic code makes it "forget" to stop growing. Once growth is turned on, cancer cells continue to divide in an uncontrolled way. It's as though you set the thermostat in your house for a certain temperature, but no matter how hot your house gets the furnace keeps running. No matter what you do to turn it off, it produces heat as if it had a mind of its own.
Doubling Times Cancer starts with one abnormal cell. That cell becomes two abnormal
cells that become four abnormal cells and so on. Cells divide at various rates, called doubling
times. Fast-growing cancers may double over one to four weeks; slow-growing cancers may double over two to six months. It may take up to five years for the duplication process to happen 20 times. By then the tumor may contain a million cells yet still be only the size of a pinhead.
So there is a "silent" period after the cancer has started to grow. There is no lump or mass. It's too small to be detected by any means now known. What is not commonly appreciated is that the silent period is considerably longer than the period when we do know a tumor is present.
After many months, usually years, the doubling process has occurred 30 times or so. By then the lump may have reached a size that can be felt, seen on an x-ray or cause pressure symptoms such as pain or bleeding. To be able to see a tumor on an x-ray, it usually has to be about 1 cm (1/2 in.) in diameter. At that stage, it will contain about 1 billion cells. When it is smaller, x-ray imaging techniques are not usually sensitive enough to detect it, although some newer imaging methods—especially computerized tomography (CT) and magnetic resonance imaging (MRI) may sometimes detect such small tumors.
