1. World Health Organization. http://www.who.int/cancer/en . Accessed 02 Dec, 2014)
2. American Cancer Society: http://www.cancer.org/docroot/stt/stt_0.asp?from=fast . Accessed 02 Dec, 2014)
3. Papac RJ, Yale J (2001) Biol Med 74:391
4. Schottenfeld D, Beebe-Dimmer JL (2005) Annu Rev Public Health 26:37
5. Frei E III, Elias A, Wheeler C, Richardson P, Hryniuk W (1998) Clin Cancer Res 4:2027