The risk of cancer is thought to be caused from both genetic and environmental factors.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/what-causes-cancer-avoidable-lifestyle-choices-blame-over-genetics
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/science-world-report
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/health
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/cancer
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/non-communicable-diseases
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/smoking