On the basis of standard laboratory tests and animal models used to screen anticancer drugs, there is little evidence to support a specific cancer-killing ability for laetrile. These investigations used numerous cultured cell lines and tumor models, and they explored the following issues: (1) whether laetrile, given alone or in combination with other substances, exhibits anticancer activity of any kind; (2) the toxic effects associated with laetrile treatment; (3) the location of laetrile breakdown in the body and how this breakdown occurs; and (4) the route(s) of excretion for laetrile and its breakdown products.
Animal studies of laetrile have used rodents,[1,2,3,4,5,6,7,8,9,10,11,12] dogs,[13,14] Reviewed in  rabbits, Reviewed in  and a cat. Early work led to the hypothesis that enzymes were necessary to release cyanide from amygdalin. When high levels of these enzymes were present, symptoms of cyanide poisoning were more pronounced. Reviewed in  In two studies sponsored by the National Cancer Institute and published in 1975, various rodent cancers (osteogenic sarcoma, melanoma, carcinosarcoma, lungcarcinoma, and leukemia) were transplanted into rats and mice.[2,3] In both studies, the animals were treated with intraperitonealinjections of amygdalin, with or without the enzyme beta-glucosidase. None of the solid tumors or leukemias investigated responded to amygdalin at any dose tested. No statistically significant increase in animal survival was observed in any of the treatment groups. Similar results were obtained in another study using human breast and colon cancercells implanted into mice (xenograft models). Amygdalin at every dose level tested produced no response either as a single agent or in combination with beta-glucosidase. It was discovered that animals experienced more side effects when beta-glucosidase was given concurrently (at the same time) with amygdalin, compared with amygdalin alone.[2,3]
Gastrointestinal stromal tumor is a disease in which abnormal cells form in the tissues of the gastrointestinal tract.
The gastrointestinal (GI) tract is part of the body's digestive system. It helps to digest food and takes nutrients (vitamins, minerals, carbohydrates, fats, proteins, and water) from food so they can be used by the body. The GI tract is made up of the following organs:
Large intestine (colon).
Gastrointestinal stromal tumors (GISTs)...
Additional cell culture and animal studies involving more than a dozen other tumor models have been published.[1,4,5,7,8,10,11,16,17,18,19,20] In one study, preliminary findings by one of the principal investigators that amygdalin inhibited the growth of primary tumors and the incidence of lung metastases in mice bearing spontaneous (not treatment-induced) mammaryadenocarcinomas could not be confirmed. However, positive results were obtained in four studies.[11,17,18,20]
In the first of these studies, amygdalin enhanced the antitumor activity of a combination of enzymes and vitamin A in mice bearing spontaneous mammary adenocarcinomas. The amygdalin was given by intramuscular injection, the vitamin A was administered orally through a feeding tube, and the enzymes were injected into and around tumor masses. No anticancer activity was observed when amygdalin was given alone.
In the second study, white blood cells and prostate cancer specimens were used to investigate the potential of amygdalin to stimulate the immune system. The researchers found that amygdalin caused a statistically significant increase in the ability of a patient's white blood cells to adhere to his own prostate cancer cells, suggesting some immune system boosting potential for amygdalin.