  Development of a tumor is known to be a result of accumulation of DNA changes
in somatic cells. However, the processes of how DNA changes are produced and
how they accumulate in somatic cells are not clear. DNA changes include two
types: point DNA mutations and chromosome changes. However, point DNA mutations
(DNA mutations) are the main type of DNA changes that can remain and accumulate
in cells. Severe DNA injuries are the causes for DNA mutations. However,
Misrepair of DNA is an essential process for transforming a DNA injury into a
survivable and inheritable DNA mutation. In somatic cells, Misrepair of DNA is
the main source of DNA mutations. Since the surviving chance of a cell by
Misrepair of DNA is low, accumulation of DNA mutations can take place only
possibly in the cells that can proliferate. Tumors can only develop in the
tissues that are regenerable. The accumulation of Misrepairs of DNA needs to
proceed in many generations of cells, and cell transformation from a normal
cell into a tumor cell is a slow and long process. However, once a cell is
transformed especially when it is malignantly transformed, the deficiency of
DNA repair and the rapid cell proliferation will accelerate the accumulation of
DNA mutations. The process of accumulation of DNA mutations is actually the
process of aging of a genome DNA. Repeated cell injuries and repeated cell
regenerations are the two preconditions for tumor-development. For cancer
prevention, a moderate and flexible living style is advised.
