Sunlight can be used to treat cancer using a method developed by University of Tokyo researchers. Their method focusses sunlight on the cancer-affected areas using optical fibres. The photochemical reaction with a previously injected substance kills cancer cells.
Cancer treatment methods, using lasers in photodynamic therapy, already exist, but the sunlight method is superior in two ways: conventional photodynamic therapy methods need laser equipment whereas sunlight can be used with various substances; and the sunlight method is much cheaper.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/sunlight-kills-cancer
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/down-earth
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/cancer
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/solar-energy
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/medical-research
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/science-and-technology
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/japan