The late, great Andreas Moritz observed that cancer itself is a cellular defense mechanism that the body employs to save the cells when they are under attack from toxins - instead of dying, the cells remain alive, multiply and ward themselves with a protective barrier. The idea is to allow the body to restore itself to proper health and eliminate the causes of cancer - toxins and unhealthy cellular terrain (as the great French scientist Antoine Bechamp told us was the cause of cancer and most other illness a century and a half ago). In today's world that is filled with toxins and poor nutrition and lack of healthy lifestyles, that can be difficult to do. In the past, all foods were organic, and the air and water were not filled with man-made toxins.
Insofar as releasing toxins, cancer cells do indeed release an overabundance of toxins when they are being killed off. Another late, great cancer figure, Max Gerson found that the release of toxins caused by his wonderful juicing protocol (which provided cellular cleansing and nutrition and resulted in the death of cancer cells) initially resulted in half of his patients dying from liver failure. Gerson observed that he never encountered a single cancer patient who did not also have an impaired liver - an observation which profoundly affected my own journey into searching for natural cancer alternative treatments). In addition to cancer cells, impaired livers are often huge depositories of toxins - especially fatty livers.
The good news is that impaired, damaged and/or diseased livers can be restored to full health and function with cleansing, good AND key supplementation. Milk thistle is an absolute must. In his clinical study Dr. Burton Berkson found that a combination of milk thistle, alpha lipoic acid and selenium were able, along with healthy changes in diet and lifestyle, to restore the livers of all three women in his limited study to full function whereas they had been facing imminent liver failure and either liver transplants or horrific and usually unsuccessful interferon treatments.