No cancer can be 100% attributed to one thing. We live in a World full of carcinogens. Anyone of them can cause cancer.
Indoor tanning, tobacco use, abestos and, many other...
According to an article, "Metastasis is the transfer of malignant tumors from one organ to a distant organ. It is the most common cause of death in cancer patients."
http://content.karger.com/produktedb/produkte.asp?typ=fulltext&file=OCL2005069S01014...