Cancer cells are formed through a complex process of transformation happening to normal cells. The first step is called “initiation”, during which the genetical substance attached to DNA molecule and chromosome structures make cells carcinogenic attribute. Genetical change can happen at random or caused by carcinogen. Carcinogenic substances include chemical substance, tobacco, rays, virus and sunlight. Not all carcinogen has the same possibility of leading to cancer. Genetical deficiency in cells will make one more susceptible to cancer. Chronic physical examination will increase the sensitivity of cells to carcinogen.
The second step and the last step in the development of a cancer are both called “promoting”. The substance that promotes this process is called promoter that can be substance in the environment or drugs. Different from carcinogen, promoter won’t lead to a cancer. Promoter provokes the carcinogenic capability of potentially stimulated cells but has little influence on cells not being stimulated. With above factors, cancer is likely to happen. In general, susceptible cells and carcinogen work together to cause cancer.
Some carcinogen can even cause cancer without any promoter. For instance, ionizing radiation (X radio, generated by the explosion of Nuclear power plant or Atomic bomb) can lead to a variety of cancer such as Osteosarcoma, leukemia, thyroid and breast cancer.
Cancer cells can grow into surrounding tissues or metastasize into other tissues or organ, near or far. Cancer can also spread in lymph system and this spread is typical in cancer metastasis. For example, Breast cancer metastasizes to lymph node nearby before it spreads to the whole body. Cancer can spread by blood and this is a typical way for a sarcoma to spread.