The news left vegetarians feeling vindicated. It sent meat producers into a tizzy. And it left many others wondering: Do bacon and bologna really cause cancer?

Two weeks ago, after a group of 22 scientists reviewed numerous studies, World Health Organization officials concluded that processed meat is carcinogenic, and that eating a couple of slices a day increases a person's risk of colorectal cancer by about 18 percent.

But like so many cancer risks, teasing out the details and maintaining perspective is crucial. In the general U.S. population, the overall risk for colorectal cancer is 5 percent. For regular bacon-eaters, the risk would rise to 6 percent. Meanwhile, having three cigarettes a day increases a person's chances of developing cancer by 500 percent.

According to a recent report by Penn's Abramson Cancer Center, almost 45,000 residents of the Greater Delaware Valley - 15 counties from Trenton to New Castle to Cape May - will be diagnosed with cancer this year, and almost 16,000 people will die as a result of cancer.

Carmen Guerra, associate professor of medicine at the Hospital of the University of Pennsylvania and associate chief of staff at Abramson, researches cancer screening and prevention. She spoke to us recently about cancer risk.

What are the greatest risk factors for cancer?

The biggest is smoking. If you looked at all cases of cancer, about 30 to 35 percent are induced by smoking. Research shows that obesity is second, causing about 20 percent of cancer cases. The third would be pathogens - bacteria and viruses - causing 15 percent. For example, people are probably familiar with human papillomavirus, HPV. It causes cervical, oral, anogenital, and head and neck cancer. We also know that some hepatitis viruses cause liver cancer.

But then you look at diet and activity, and those are only 5 percent contributors to the overall cancer incidence. Alcohol is about 4 percent. So a glass or two of wine with dinner is one thing, but smoking is much more risky.

What about genetic factors?

A lot of people believe that if they don't have a family history, they're not at risk for a particular cancer. I keep hearing that in my office. But this is a misconception. The majority of cancers happen in people without a family history. Specifically, about 85 percent of women who get breast cancer do not have a family history of the disease, according to the American Cancer Society.

Is it possible to determine individual risk?

This is such a complex topic, even for doctors. It really is a field that is developing. We don't have all the answers. But research has given us some answers, and to some extent, rough estimates of cancer risk.

One of the most important things research has given us is calculators to assess individual cancer risk. They are on a National Institutes of Health website.

The Breast Cancer Risk Assessment Tool is at www.cancer.gov/bcrisktool/. This one is the most accurate. You can put in age, family history, personal history, etc., and out comes an estimate of your risk for developing breast cancer in the next five years and over your lifetime. And it gives you a comparison to the general population.

The Colorectal Cancer Risk Assessment Tool is at www.cancer.gov/colorectalcancerrisk/.

Other tools - some are still in development or waiting to be validated by research - are at http://epi.grants.cancer.gov/cancer_risk_prediction/.

While we've come a long way, the calculators are not perfect. They are often for women and men who are at "average risk," as they call it. So not all populations are included. The calculators don't incorporate emerging risk factors that we're just beginning to learn about. They don't get updated as often as I might consider ideal. But for a rough estimate, they're good.

On the provider's end, assessing personalized risk is certainly the goal. Embedding the calculators into electronic records will be a wonderful way to put this into practice.

If you learn your risk, what then?

It's pretty powerful to look at information about yourself and see where you fare against the average population, and that it's no longer a theoretical risk. It becomes more real, more tangible, and potentially motivates behavior more. But I wouldn't want patients to become frightened. It would be important to have a professional provider say, "OK, let's talk about strategies."

Getting back to the bacon, which is not in the risk calculators, can we eat it or not?

There was a lot of science before the WHO announcement that raised the possibility that processed foods put patients at risk. This was just additional evidence that we have been waiting for, frankly, to be more decisive about how to advise our patients. We have been advising them to avoid high-fat foods. Now, it's a matter of avoiding processed foods.

People like their bacon, their sausage. I have patients who eat two slices of bacon a day. The report seems to have frightened a lot of people. There were a lot of calls. Many of them wondered, "Do I really need to stop?"

But if they also smoke, the most important thing they could do would be to stop smoking. It's a new world where your bacon makes it to the list of carcinogens.