Chemotherapy focuses on destroying cancerous cells (along with healthy cells) whereas nutrition focuses on giving the body what it needs to make healthy cells again. You don't necessarily have to kill cancer cells with drugs or radiation if you can:
1- get the body to start making healthy cells again by giving it the nutrients it lacks and
2- rebuild the mechanisms in the body that destroy cancerous cells but have been disabled due to malnutrition.
We can say that cancer is generally caused by putting lots of toxins into the body while depriving the body of the nutrients it needs to run the systems that neutralize these toxins. This is exactly what the Standard American Diet does. Stress and other less tangible factors are also toxic to the body and can incapacitate and destroy, sometimes beyond repair, crucial protective mechanisms and even entire glands.
The body literally makes millions of cells every hour. Every single cell in the GI tract is replaced every 3-5 days and most cells in the body are replaced at least every three weeks! And as you might imagine, replicating a million healthy cells every hour requires a constant supply of many nutrients. Cell replication is impaired when the nutrients necessary for healthy cell replication are absent, which in turn leads to mutations and cancer.
Cancer is one possible end result of chronic malnutrition. There are many others, but they are all "lifestyle diseases" caused by what is often very treatable and preventable malnutrition. Give the body what it needs to protect itself and the odds you'll ever need cancer treatment - natural, drug-based, or otherwise - become very low.