You would better off reading a review or a book on the subject to understand the evolutionary grounds for cancer development; the field is pretty complex and controversial.

The 2 major theories for cancer progression that i known of are the clonal diversification model and the Cancer Stem Cell model.

A third theory is this idea that infectious agents are response for cancer development, "Germ theory of disease."

The basic idea is understanding how natural selection is involved in malignant neoplastic development. For this to occur cancer cells must be able to survive a harsh environment consisting of an array of immune defenses and evade cell programmed cell death; only cells with certain genetic alterations and defenses are able to accomplish this feat.

many thanks of you, sure, I want to read "cancer, the evolutionary legacy" was written by "Mel Greaves", that is complex subject in Biology of cancer

the key to understand the cancer evolution is to study the unique evolutionary pattern of cancer.

See the following link:

http://www.ncbi.nlm.nih.gov/pubmed/21925306

The idea that cancer evolution represents a throwback to ancient evolutionary pathways is questionable; referring to the davies model. Sure, many of the pathways active in tumor cells may resemble ancient counterparts; they are also resemble some present day pathways during embryonic development as well. But cancer cells do not function the same way these ancient cells function.

However, it is helpful to view cancer in an evolutionary light

A deeper question to answer is what is the evolutionary advantage to somatic cells moving into an ancient state? For that