The World Health Organization considered more than 800 different studies on cancer in humans.
The study concluded that eating processed meat causes cancer. Processed meats have been classified in the same category as causes of cancer such as tobacco smoking and asbestos.
According to the Global Burden of Disease Project, an independent academic research organization, about 34 000 cancer deaths per year worldwide are attributable to diets high in processed meat.
Here's an article from the American Cancer Society discussing it.