Try not to take this too seriously, I'm not educated in cancer research or have a degree/diploma in medical science, also I'm only 22 and sometimes like to believe I'm smarter than I probably am.
I've pondered on the thought of what could be the cause of cancer, I have always believed that we are causing it, or at least increasing the occurence.
I believe the cause of cancer is the abundance of low levels of toxic substances in the air, the substances which scientists have led us to believe are "safe" in small quantities, each substance has slightly raised the occurence of the cells malfunctioning.
Evidence of cancer has been found in remains of humans from thousands of years ago, yet it has not shown the prevalence, I believe that the malfunction which causes the cells to duplicate is natural, it is a fault with our DNA, however how often it occurs is not and is a fault of our own.
This would explain why over 2000 substances have been proven to cause cancer, because many substances will cause cells the need to regenerate, increasing how often the cells need to regenerate increases the likelihood that the fault will occur.
This may not be the cure for cancer, but if it were to be true then it would be the cure for the cancer pandemic.