Killing old cells and replacing it with same number of normal new cells is ongoing process. While producing new cells few abnormal cells are also produced. Body has a very efficient quality control department. As new cells are produced quality control department checks each and every cell and allows only normal cells to enter in the new cycle, abnormal cells are killed and not allowed to enter in the new cycle.
Now any defect in above process produces cancer. If quality control becomes weak due to genetic defects or old age or decreased immunity chances of defective cells entering to new cycle increases. Once defective cell enters new cycle it keeps on producing new defective cells and tumour or cancer is formed. E.g. Familial cancers, old age cancers, cancers with AIDS.
If production of cells is more due to continuous infection (H. Papilloma virus in carcinoma cervix) or due to continuous injuries and healing (betel nut injuries in oral cancer) or action of carcinogens on developing new cells (tobacco in oral cancer) chances of abnormal cells entering to new cell cycle and developing cancer increases.
- TOBACCO – CHEWING OR SMOKING
- DIET AND EXERCISES
- VIRAL INFECTIONS