These Johns Hopkins researchers have been presenting this quite radical, IMO, theory for a year or more now. It's really quite astonishing to propose that:

"...random, unpredictable DNA copying "mistakes" account for nearly two-thirds of the mutations that cause cancer."

If luck is the leading cause of cancer, how do screen for this?

Interesting study but I'm not convinced it is accurate. I certainly agree there are many people who live a healthy life style regarding diet, exercise, weight and still get cancer. I still believe exposure to environmental contamination and toxins play a significant role. A person could have had early childhood exposure and then developed a cancer many years later as these gene mutations occur. I would be curious to know more information collected for these people/patients regarding where they lived and their childhood exposure. I still believe this environment exposure is higher than they are reporting.

You really need to read the article and study the examples to understand what they are saying. Here's the original full article:

Stem cell divisions, somatic mutations, cancer etiology, and cancer prevention

And here are the data tables, including Table S6, which has the info about breast cancer: Supplementary Materials

To use Lung Cancer as an example (since it's the example explained in most detail in the article), what the authors are saying is that even though 89% of lung cancers are preventable by eliminating certain environmental factors, 35% of lung cancers areactually caused by replicative cell errors. This is because there 3 different ways that lung cancer might develop. In some cases, it develops strictly as a result of exposure to environmental factors. In a small percent of cases, it develops strictly as a result of replicative cell errors. And some cases, it develops as a result of a combination of both environmental exposure and replicative cell errors. In total, 35% of all lung cancer cases are at least in part caused by replicative errors; in these cases, if the cell mutation error had not occurred, the cancer would never have developed (even if there was environmental exposure). This is explained in Fig. 2.

For breast cancer, Table S6 shows that "E" (environmental) is 15.1%, "H" (hereditary) is 1.5% and "R" (replicative, i.e. random cell mutations) is 83.4%. Given how the authors have developed these figures, the environmental figure seems reasonable to me, but the hereditary number seems very low, even recognizing that most hereditary breast cancers likely also include a replicative cell mutation error.

Personally I would have expected the findings to be more in the range of 15% Environmental, 10% Hereditary, and 75% Replicative. And if breast cancer were to be represented similarly to the lung cancer, pancreatic cancer and prostate cancer examples in Fig. 2, I would expect that most of the cases that include the "E" and "H" factors would also include some "R". In other words, it's my belief that environmental and hereditary factors are rarely the sole cause for the development of breast cancer, but instead act in combination with replicative errors to cause the breast cancer to develop. And that seems to be the basic premise of what the authors are saying about many types of cancers.

Agree with Beesie that the H seems low; so many posters have family history without any (known) genetic markers for cancer. It's possible that the study adjusted for that by including a factor for family incidence, but if only genetic test results were considered, the incidence of cancer attributable to H would be falsely low. I am admittedly a science idiot, but I am also having trouble sussing "normal" Replication errors from those caused by E. Any data used is necessarily a snapshot it time, so whatever the baseline for "normal" R errors would need to be refigured periodically in order to be aware of an uptick. The rate of aggressive BC in young women has been rising (article linked); how does a study like this explain that? The answer will likely be environmental triggers that are new in our time. Figuring out what they are is the tricky part. http://jamanetwork.com/journals/jama/fullarticle/1656255