Initial studies at Sloan-Kettering
In 1972, Memorial Sloan-Kettering Cancer Center (MSKCC) board member Benno C. Schmidt, Sr. convinced the hospital to test laetrile so that he could assure others of its ineffectiveness "with some conviction."[28] Kanematsu Sugiura, the scientist who performed the requested tests, found that laetrile inhibited secondary tumors in mice, though it did not destroy the primary tumors. He repeated the experiment several times with the same results. However, three other researchers were unable to confirm Sugiura's results. While these uncontrolled and inconclusive results were considered too preliminary to publish, they were leaked to laetrile advocates, resulting in significant public attention.[28]
To expand on Sugiura's results, MSKCC researchers conducted a controlled experiment in which they injected some mice with laetrile (as Sugiura had done) and others with placebo. Sugiura, who was unaware of which mice had received laetrile, performed the pathologic analysis. In this controlled, blinded follow-up of Sugiura's initial uncontrolled experiment, laetrile showed no more activity than placebo.[28]
Subsequently, laetrile was tested on 14 tumor systems without evidence of effectiveness. Given this collection of results, MSKCC concluded that "laetrile showed no beneficial effects."[28] Mistakes in the MSKCC press release were highlighted by a group of laetrile proponents led by Ralph Moss, former public affairs official of MSKCC who was fired following his appearance at a press conference accusing the hospital of covering up the benefits of laetrile.[29] These mistakes were considered scientifically inconsequential, but Nicholas Wade in Science stated that "even the appearance of a departure from strict objectivity is unfortunate."[28] The results from these studies were published all together.[30]
Subsequent clinical studies
A 2011 systematic review from the Cochrane Collaboration found:
The claims that laetrile or amygdalin have beneficial effects for cancer patients are not currently supported by sound clinical data. There is a considerable risk of serious adverse effects from cyanide poisoning after laetrile or amygdalin, especially after oral ingestion. The risk–benefit balance of laetrile or amygdalin as a treatment for cancer is therefore unambiguously negative.[31]
An earlier 2006 systematic review had concluded: "The claim that [l]aetrile has beneficial effects for cancer patients is not supported by data from controlled clinical trials. This systematic review has clearly identified the need for randomised or controlled clinical trials assessing the effectiveness of [l]aetrile or amygdalin for cancer treatment."[32]
Given the lack of evidence, laetrile has not been approved by the U.S. Food and Drug Administration.[15]
The U.S. National Institutes of Health evaluated the evidence separately and concluded that clinical trials of amygdalin showed little or no effect against cancer.[23] For example, a 1982 trial of 175 patients found that tumor size had increased in all but one patient.[33] The authors reported that "the hazards of amygdalin therapy were evidenced in several patients by symptoms of cyanide toxicity or by blood cyanide levels approaching the lethal range."[7]
The study concluded "Patients exposed to this agent should be instructed about the danger of cyanide poisoning, and their blood cyanide levels should be carefully monitored. Amygdalin (Laetrile) is a toxic drug that is not effective as a cancer treatment". |