Most cancer is bad luck, study finds

**Zippyjuan** · 01-01-2015, 01:28 PM

http://www.utsandiego.com/news/2015/...setti-hopkins/

Nearly two-thirds of all cancers are caused by random mutations of the body's stem cells, not by hereditary or environmental effects, according to a study released Jan. 1 by Johns Hopkins scientists.

Tissues with the most divisions of regenerative cells -- and hence the most chances for mutations -- tend to have the greatest rates of cancer, the study found.

This explains why skin cancers, for example, are far more common than bone cancers. Skin cells die constantly, so they must be replenished far more often than those that make bone, introducing more chances for errors that lead to cancer.

In effect, most cancers come down to "bad luck", the researchers say in the study, which can be found at http://www.sciencemag.org/content/347/6217/78

The findings introduce new dimensions to the struggle against cancer, said two researchers who did not take part in the study.

-- If most cancers are caused by random mutations that can't be prevented, early detection is greatly important.

-- It supports the theory of cancer stem cells, that a few aberrant cells seed the vast bulk of tumors and are especially dangerous. If these stem cells aren't eliminated, the cancer will return.

-- Finally, modern cancer therapy, which tends to focus on the genetic cause of the disease rather than the tissue in which it originates, may need to take a harder look at the cell types from which cancers spring in developing therapies.

The study was published Thursday in the journal Science. Cristian Tomasetti of the Johns Hopkins Kimmel Cancer Center at Johns Hopkins Medicine in Baltimore is first author. The study's senior author is Bert Vogelstein, also of the center, part of Johns Hopkins University.

Healthy diet and protection against carcinogens are still important, said Tomasetti, because the one-third variability is still substantial. And the proportion of randomness in each type of cancer varies. Some cancers tend to be greatly increased by environmental factors, such as lung cancer in smokers. The two-third average is a summary of the risk of cancer from all tissue types.

Strong relationship

The study examined the frequency of cell divisions in 31 tissue types over an average person's lifetime, compared with the lifetime incidence of cancer in those 31 tissues. The linkage was strong; with a linear correlation of 0.81. When that number is squared, a basic step in statistical analysis, it yields 0.65. In other words, 65 percent of the difference in cancer frequencies among cell types can be attributed to the number of stem cell divisions.

More at link.

**Ronin Truth** · 01-01-2015, 04:29 PM

I'd SWAG heredity and life style choices.

**donnay** · 01-01-2015, 05:36 PM

Epigenetics plays a key role in cancer.

Epigenetics

There exist several definitions of epigenetics, and as a result, there are disagreements as to what epigenetics should mean. Epigenetics (as in “epigenetic landscape”) was coined by C. H. Waddington in 1942 as a portmanteau of the words epigenesis and genetics. Epigenesis is an old word that has more recently been used (see preformationism for historical background) to describe the differentiation of cells from their initial totipotent state in embryonic development. When Waddington coined the term the physical nature of genes and their role in heredity was not known; he used it as a conceptual model of how genes might interact with their surroundings to produce a phenotype.

Robin Holliday defined epigenetics as “the study of the mechanisms of temporal and spatial control of gene activity during the development of complex organisms.” Thus epigenetic can be used to describe anything other than DNA sequence that influences the development of an organism.

The more recent usage of the word in science has a stricter definition. It is, as defined by Arthur Riggs and colleagues, “the study of mitotically and/or meiotically heritable changes in gene function that cannot be explained by changes in DNA sequence.” The Greek prefix epi- in epigenetics implies features that are “on top of” or “in addition to” genetics; thus epigenetic traits exist on top of or in addition to the traditional molecular basis for inheritance.

The term “epigenetics”, however, has been used to describe processes which haven’t been demonstrated to be heritable such as histone modification, there are therefore attempts to redefine it in broader terms that would avoid the constraints of requiring heritability. For example, Adrian Bird defined epigenetics as “the structural adaptation of chromosomal regions so as to register, signal or perpetuate altered activity states.” This definition would be inclusive of transient modifications associated with DNA repair or cell-cycle phases as well as stable changes maintained across multiple cell generations, but exclude others such as templating of membrane architecture and prions unless they impinge on chromosome function. Such redefinitions however are not universally accepted and are still subject to dispute.

In 2008, a consensus definition of the epigenetic trait, “stably heritable phenotype resulting from changes in a chromosome without alterations in the DNA sequence”, was made at a Cold Spring Harbor meeting. From Wikipedia, the free encyclopedia