In the above article, they have summarized that most cancers occur without any cause as such, in other words - a bit of a bad luck.
What they are trying to say is, in our bodies billions of cells are present and any one of them can undergo a 'cancerous' change without any reason as such. Of course, in 99.99% people, the body's defense mechanisms will recognize and destroy these cells and cancer wont form. If, for some reason, the body's defense fails, the cancerous cell which was formed will multiply and give rise to cancer.
The reason of sharing this article is that, when cancer occurs, most of us always think, why did it occur? What was the problem with me, or what did I do wrong? And the answer remains, that we did not do anything wrong; just that it happened because it had to happen. The more important thing is that, it was good that we caught it early.