On Christmas day, I had my family over for the annual holiday dinner. I sat near my 15-year old niece, and we talked of roller coasters and her experiences driving since now that she has her learner’s permit. Then she asked me to explain how cancer forms. Her high-school biology teacher had tried explaining it to her, but it wasn’t done in a way that was understandable to my niece and her friends. So I gave it a shot, in the way I usually explain to patients.

Essentially, I told her that cancer forms when the genetic material (DNA) in one cell goes awry, causing the cell to divide without stopping or without the cell undergoing its natural cell death (apoptosis). The one cell turns into 2 cells, then those 2 cells turn into 4 cells, then the 4 cells multiply into 16 cells, and so on. Eventually the group of cells is big enough to form a cancerous tumor. If the body’s immune system is not strong enough to detect those cells-gone-wrong – or even if it is strong enough, but maybe another mechanism is in place – the cancerous growth will continue and eventually cause problems for whatever organ or tissue it is growing in.

Then my niece asked me the tough question. “So why does cancer form in the first place?”

And that is the million dollar question. Or trillion dollar question, really.

We know that some cancers are caused by infections — such as cervical cancer which is caused by strains of the human papillomavirus (HPV) or liver cancer caused by the hepatitis B or hepatitis C virus. Smoking clearly causes some types of cancer – lung cancer and some types of head and neck cancers, for example. Radiation exposure can lead to cancer, since radiation inherently damages the genetic material – the DNA – in healthy cells.

But what about diet? What about the things we eat and drink on a daily basis?

This is a much harder question to answer. I’ve delved into the medical literature on the role of diet and cancer, and the the information there is about as clear as brackish swamp water.

This morning, I read this blog post and I think it is a nice guideline to follow for healthful eating. While there are no hard and fast rules of thumb listed, the post makes some general recommendations based on what research currently exists.

I think a nice approach to viewing cancer-causing substances is this: Some things are definitely “high risk” and should be avoided — smoking definitely falls into this category. Other things fall into the “moderate risk” group, and perhaps these are the ones that cause us the most angst — red meat, processed meats (such as cured or smoked meats), and alcohol are the first few that come to mind. The items in the “moderate risk” group are those that we want to be able to enjoy – and we can – but we shouldn’t have them too often. Of course, “too often” is often a debatable amount of time.

Very unsatisfying, right? I completely agree.

And in the end, I’m not sure I cleared up anything for my niece, but hopefully she’ll at least pass the cancer section of her next biology test.