Congratulations on coming back from stage IV cancer.  The idea of laetrile working because it kills parasites is an interesting one, and it may indeed work that way at time. However, the idea that cancer is always caused by parasites is not a valid one in my opinion, any more than the other handful of universal causes of cancer that have been put forth (such as cancer is a fungus, Hulda Clarke's mysterious flukes, etc.).

Cancer, in my opinion, is caused by an irritation and resultant inflammation that results in the formation of mutated cancer cells that are able to defeat the immune system and gain purchase in the body as a growing mass of cancer cells.  Such irritation might be from a toxin, viral infection, bacterial infection, and yes, even parasites.

Laetrile works for some cancers much better than others.  Fortunately, those cancers include most of the major ones

So how does B17 kill cancer?...... Here we go....

Firstly we need to understand that our bodies use several enzymes to perform many tasks. Our body has one particular enzyme called Rhodanese which is found in large quantities throughout the body but is not present where ever there are cancer cells. Yet, where ever you find cancer in the body, you find another enzyme called Beta-Glucosidase. So, we have the enzyme Rhodanese found everywhere in the body except at the cancer cells, and we have the enzyme Beta-Glucosidase found in very large quantities only at the cancer cell but not found anywhere else in the body. If there is no cancer in the body there is no enzyme Beta-Glucosidase.

Now the following is what scares most people. You see, Vitamin B17 is made up of 2 parts glucose, 1 part Hydrogen Cyanide and 1 part Benzaldehyde(analgesic/painkiller). So its very important you understand the following:

When B17 is introduced to the body, it is broken down by the enzyme Rhodanese. The Rhodanese breaks the Hydrogen Cyanide and Benzaldehyde down into 2 by-products, Thiocyanate and Benzoic acid which are beneficial in nourishing healthy cells and forms the metabolic pool production for vitamin B12. Any excess of these by-products is expelled in normal fashion from the body via urine. Vitamin B17 passes through your body and does not last longer than 80 minutes inside your body as a result of the Rhodanese breaking it down. (Hydrogen Cyanide has been proven to be chemically inert and non toxic when taken as food or refined pharmaceutical such as laetrile. Sugar has be shown to be 20 times more toxic than B17 - see good & bad cyanide).

HERE IS THE GOOD PART - When the B17 comes into contact with cancer cells, there is no Rhodanese to break it down and neutrelise it but instead, only the enzyme Beta-Gucosidase is present in very large quantities. When B17 and Beta-Glucosidase come into contact with each other, a chemical reaction occurs and the Hydrogen Cyanide and Benzaldehyde combine synergistically to produce a poison which destroys and kills the cancer cells.

This whole process is known as selective toxicity. Only the cancer cells are specifically targeted and destroyed. See the diagram below.

That is how Vitamin B17 Kills Cancer. It has been proven and illustrated to work by the some of the top specialists in the world. Thats why the Contreras hospital in Mexico have been able over the LAST 30 YEARS to successfully treat over 100,000 cancer patients!!!

http://www.laetrile.com.au/copy.asp?sect=q1&page=howdoes

Webster Kehr, at the Cancertutor.com, has some good information and acvice about laetrile:

http://www.cancertutor.com/Cancer/Laetrile.html

And this section I believe is very important:

Supercharging This Treatment

Unless you are using high doses of a quality source of laetrile, you should not DEPEND on laetrile as the core treatment in a cancer treatment program. Treat this as a supplemental treatment or a remission treatment.

Either way, it is necessary to use one of the major treatment articles as a base of operations or as a supplement to high doses of laetrile:
Treatment For Stage I, II and III Cancer Patients
Treatment For Stage IV Cancer Patients