Processed meat (meat cured, smoked or similarly treated to enhance preservation and/or flavour, which includes ham, bacon, frankfurts, salami, and the like) has been classified by the World Health Organisation into the same category of recognised causes of cancer as asbestos, tobacco, arsenic and alcohol.
This doesn't mean that eating processed meat puts you at the same risk of developing cancer as tobacco smoke and asbestos, just that the strength of evidence for cancer causation is comparable.
"Lifetime smoking increases risk of lung cancer 50-fold. But worst case scenarios in relation to processed meat or red meat rarely reach more than two-fold. ... Experts concluded that every 50-gram portion of processed meat daily (that’s two slices of bacon) increases the risk of bowel cancer by 18%.
Red meat ranked lower, in group 2A. It was evaluated as probably carcinogenic to humans, possibly causing bowel cancer. It was also implicated in pancreatic and prostate cancers."
Bernard Stewart, Professor, Paediatrics, Cancer and related disorders, Epidemiology, Biochemistry and Cell Biology , UNSW Australia puts yesterday's WHO announcement into context:
Given our increased risk of developing secondary cancers with CLL, that doesn't mean we should drop processed meat and alcohol from our diet, but perhaps we may decide to reduce our consumption slightly.