Many cancers really aren't avoidable, as there's a spectrum of causes. The mutations that cause cancer can come from many sources - carcinogen exposure, UV light/radiation, inherited defects, or unavoidable errors that occur when cells divide (on average, around 3 errors per cell division).

Getting cancer is a lot like playing the lottery (or perhaps more accurately, Russian Roulette). It requires an accumulation of mutations in two or more key genes, and these mutations occur more or less randomly throughout the genome, regardless of cause. So maybe your first hit happens from a chest X-ray, and the second hit comes from smoking. Or maybe you just get old and the replication errors pile up in blood stem cells, giving you leukemia.

The point is that it's all probablistic, and that's why some smokers live to be 100 cancer-free, and some health-nut marathoners get cancer. In general, though, these external factors can bend the odds one way or the other.

While still (probably) probabilistic to a large extent, specially concerning environmental exposure, there's more acceptance recently into cancer having a metabolic component, many cancer and metabolic related pathways cross (eg fasting/insulin/igf-1). So it's not necessarily just lottery, or rather, we still don't know how large of an factor the lottery part actually is.

very well said, this can be copied to all those articles about food causing/not causing cancers that seem to pop up recently. not much more is needed to know on this topic

Just one example: About 12 percent of women in the general population will develop breast cancer sometime during their lives. By contrast, according to the most recent estimates, 55 to 65 percent of women who inherit a harmful BRCA1 mutation and around 45 percent of women who inherit a harmful BRCA2 mutation will develop breast cancer by age 70 years. These estimations are a bit in flux, I've heard much higher ones in the past.

(http://www.cancer.gov/about-cancer/causes-prevention/genetic...)

> If 45% are preventable, then are the rest NOT?

We will find out more causes of cancer as time goes on. And then more will be preventable. I am sure that environmental pollution causes are a big one that isn't included in this report -- and also various chemicals we encounter in our daily lives (soaps, etc) are likely contributing to cancer as well.

Ordinary soap? That seems like a stretch.

There are a ton of additives that have been in soaps and shampoo that can cause cancer...

https://www.healthline.com/health-news/cancer-dangerous-chem...

http://www.medicalnewstoday.com/articles/285641.php

http://www.mirror.co.uk/lifestyle/health/breast-cancer-fears...

http://www.cancer.gov/about-cancer/causes-prevention/risk/su...

And I am sure that over time there will be more things in our environments that we are regularly exposed to that will be identified as cancer causing, although it is hard to predict which ones.

How about the notion that we've figured out all the causal links/factors for the different kinds of cancer?

>does it really mean most cancers are just not preventable?

It really makes me want to go eat some bacon and cheetos.