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En excerpt from the book : 

by Ross, R.Ph. Pelton, Lee Overholser

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LAETRILE THERAPY is probably the best known and most widely publicized of alternative cancer therapies. Laetrile, more than any other substance, epitomizes the scientific and philosophical controversy that has raged between supporters of alternative cancer therapies and the medical establishment.


Amygdalin is a member of a group of cyanide-containing substances called nitrilosides, which occur naturally in plants. The terms laetrile and amygdalin are often used interchangeably. Laetrile is a concentrated extract of amygdalin prepared from apricot kernels specifically for cancer therapy. The extraction process was developed by Dr. Ernst Krebs, Jr., who pioneered the use of laetrile in cancer therapy. (17)

Amygdalin, which is also called vitamin B17, is a relatively simple compound that occurs naturally in much of our food supply. Substantial amounts of amygdalin are found in apricots, peaches, cherries, berries, buckwheat, millet, alfalfa, and some strains of beans and peas. It is estimated that it occurs in about 1,200 different kinds of plants, with the highest levels occurring in the seeds of non-citrus fruits.

When laetrile (or amygdalin) is acted upon by the enzyme beta-glucosidase, it breaks down into two molecules of glucose (a sugar), one molecule of benzaldehyde (an analgesic), and one molecule of hydrocyanic acid (a poison).

As the enzyme beta-glucosidase breaks amygdalin down into its component parts, toxic cyanide is released. Studies have shown that various types of cancer cells contain from 100 to 3,600 times more of this enzyme than noncancerous cells, so much greater amounts of cyanide are released where there are active cancer cells. (4)

Although most cancer cells have high levels of beta-glucosidase, they are deficient in most other enzymes, especially rho-danese. (7) Rhodanese detoxifies hydrocyanic acid into nontoxic thiocyanate. Ultimately, the cyanide ion becomes part of the vitamin Bi2 molecule (cyanocobalamin). Since cancer cells have difficulty metabolizing cyanide, it is selectively toxic to cancer cells when released from laetrile. (2)

Benzaldehyde, which is a known analgesic, is also released by the breakdown of laetrile at tumor sites. This probably accounts for the pain relief that patients often report with the administration of laetrile. (8) Some research conducted in Japan has shown that benzaldehyde also has antitumor activity. (9, 11)

In theory, laetrile may be the perfect chemotherapeutic agent. It selectively destroys cancer cells and it is nontoxic to normal cells.

Animal Studies

In a study sponsored by the McNaughton Foundation in San Ysidro, California, laetrile was injected into laboratory animals intraperitoneally in dosages of 500 mg/kg. The mean survival time of the laetrile-treated animals was 70 percent longer than that of the controls. This research was reported at Senate subcommittee hearings on laetrile in July 1977. (21) In addition, studies conducted at the Pasteur Institute in Paris, using a mouse model with adenocarcinoma, showed that laetrile-treated mice survived over twice as long as the control mice. (15)

The Manner Studies

In September 1977 Dr. Harold W. Manner, chairman of the Department of Biology at Loyola University in Chicago, released to the world the results of some remarkable laetrile research. In mice prone to developing breast cancer, Dr. Manner found that laetrile in combination with vitamin A and pancreatic enzymes produced a very high cure rate. Of eighty-four treated mice, seventy-five underwent complete regression of mammary tumors, while the other nine mice showed partial regression. (10)

Dr. Manner has often been criticized for announcing the results of his research publicly instead of waiting for publication in a scientific journal. Peer-reviewed journal publication can often take as long as eighteen months, and Dr. Manner reportedly felt that this information was so important that he decided to bypass the time delay required for scientific publication and to break the story publicly.

The Sloan-Kettering) Cover-up

Ralph W. Moss gives an excellent overview of the political and scientific controversy that has surrounded laetrile in his book The Cancer Industry. He states, "Although spokespersons for orthodox medicine continue to deny that there have been any animal study data in favor of laetrile, this is contradicted by a number of studies, including—but not limited to—those at Sloan-Kettering." (15)

Moss should know, because he was discharged by the Memorial Sloan-Kettering Cancer Center when he revealed an apparent cover-up by authorities at Sloan-Kettering of positive findings about laetrile.

Dr. Kanematsu Sugiura

In the 1960s Dr. Kanematsu Sugiura, one of the world's most widely known and most highly respected cancer research scientists, officially retired from Sloan-Kettering. He continued to carry out cancer research as an emeritus associate. Ten years after his official retirement, officials at Sloan-Kettering asked Dr. Sugiura to begin testing laetrile.

Researchers at Sloan-Kettering had already found laetrile to be ineffective in animal models with transplanted tumors. However, Dr. Sugiura pointed out that laetrile could not be expected to be effective against transplanted tumors.

Dr. Sugiura's research showed that laetrile had a substantial effect on inhibiting the growth of secondary tumors in mice, although it did not destroy the primary tumors. He also reported that some of his studies showed that laetrile can produce a 60-percent reduction in lung metastases. The laetrile-treated mice appeared healthier and more active than the saline-treated controls. This would support some of the claims that laetrile can improve the quality of a patient's life.

Dr. Richard Passwater also reported that some of the positive findings in Sloan-Kettering's laetrile studies were selectively not reported. Also, it appears that some of the laetrile research was deliberately designed to fail. (18)

Controversy and Confusion

According to Ralph Moss, who worked at Sloan-Kettering for several years before being discharged, five years of testing laetrile at Sloan-Kettering ended in controversy and confusion—not a pleasing outcome for the leaders of the world's most prestigious private cancer center. In summary, about twenty experiments with laetrile produced positive results, while only a few experiments produced negative findings.

The contradictory findings and the controversy surrounding laetrile was creating a problem at Sloan-Kettering. A group of dissenters within Sloan-Kettering, who called themselves Second Opinion, wrote a memo on the subject of releasing results of the laetrile research:

If on the one hand, they publish the truth about laetrile, they will have to say something like this: we have been unable to reach any definitive conclusion on this substance. Dr. Sugiura, one of the most experienced researchers, has done many studies showing positive effects. Other researchers have claimed negative results. We think this issue can only be settled through a study on willing human volunteers with cancer, and we would like to conduct such a study here at Memorial Sloan-Kettering.

That would be honest, but it would also be disastrous from a fund-raising point of view, since it would bring down the wrath of the American Cancer Society, and the National Cancer Institute, from whom MSKCC receives most of its research funds, not to mention the Food and Drug Administration....

The other choice is to publish a totally one-sided report. ... This is the most likely prospect.... (15)

There was increasing pressure on Sloan-Kettering to release their findings on laetrile.

Sloan-Kettering's Laetrile Report

Finally, at a press conference in June 1977, Sloan-Kettering officials announced to the world the results of over five years of laetrile research. The verdict on laetrile from the respected laboratories of the world's most prestigious cancer research center turned out to be completely one-sided and negative.

Some of the comments by Sloan-Kettering's top administrators at the laetrile press conference (13) were:

We have no evidence that laetrile possesses any biological activity with respect to cancer, one way or the other.  —Lewis Thomas, president of Sloan-Kettering

We have no reproducible evidence that amygdalin, or laetrile, is active. —Robert Good, director of Sloan-Kettering

Laetrile has been found absolutely devoid of activity, period. —Daniel Martin, prominent cancer researcher

Essentially, laetrile was pronounced completely ineffective in treating cancer, despite considerable evidence to the contrary.

Worldwide Research

Research has continued in other countries, where the PDA and NCI have much less influence. Dr. David Rubin of Israel has reported using high dosages of laetrile (70 gm/day) and getting good results with breast cancer and bone cancer patients, though leukemia patients did not respond. (19)

Dr. Manuel D. Navarro, professor of medicine and surgery at the University of Santo Tomas in the Philippines, is one of the world's leading advocates of laetrile. In 1962 he presented a paper at the Eighth International Cancer Congress, describing several case histories and reporting that much higher doses of laetrile than previously used were proving to be much more effective. (16)

HCI Studies

In 1978 the National Cancer Institute published the results of a retrospective case review oflaetrile-treated cancer patients, asking for documented case histories of patients who had benefited from laetrile. (3) However, the selection criteria were so strict that almost all the reports were rejected and the study was inconclusive.

Despite these disappointing results, NCI decided to proceed with prospective clinical trials, which were conducted by the Mayo Clinic. After a Phase I trial examining dosage and toxicity, a Phase II trial, involving 178 patients with advanced cancers, was conducted. This study, published in the New England Journal of Medicine in 1982, claimed that laetrile was ineffective as a treatment for cancer. (14)

Laetrile advocates pointed out that many of the patients selected for the trial (66 percent) had already been subjected to toxic chemotherapy. Another important question involved the quality of the laetrile being used in the study. In an effort to ensure a proper trial, one of the clinics using laetrile offered to provide free laetrile of known quality for the study. This offer was refused. Dr. James Cason of the University of California at Berkeley reportedly tested the substance used in the NCI study and found that it did not contain any amygdalin (laetrile). (18)

Robert Bradford, founder of the Committee for Freedom of Choice, stated, "The whole thing, as far as we are concerned, is a put-up to discredit laetrile." At this time it appears laetrile has not yet received a fair, unbiased trial.

Current Status

Laetrile therapy is one of the first alternative cancer therapies that tended to polarize the emotional issue of freedom of choice for Americans in health care. It became a fight between the "quacks" and the medical establishment.

Laetrile is one of the naturally occurring substances that cannot be patented, making it a true orphan drug. No drug company is interested in committing money to research laetrile's potential. The only answer is good, unbiased government-sponsored research without the type of controversy that accompanied the Sloan-Kettering studies.

Another problem with setting up appropriate research studies is that laetrile is not meant to be a stand-alone therapy. Proponents of laetrile have always emphasized that it is effective only when used in conjunction with a healthy diet, pancreatic enzymes, and nutritional supplements.

There are thousands of patients who have been treated with laetrile in the past thirty years or so. I have personally met many individuals who claim that laetrile was primarily responsible for curing them or one of their family members. However, it must be emphasized that anecdotal evidence is not scientific proof.

Some alternative cancer clinics use laetrile regularly and claim to have a steady stream of patients who respond well. On the other hand, there do not appear to be overwhelming numbers of laetrile-cured cancer patients. It seems that laetrile has become just one of many ingredients in holistic cancer treatment programs.

The published research seems to indicate that laetrile does have a role to play. It is probably more effective with early-stage cancers rather than with terminally ill patients. It is apparently more effective when used together with other factors. In summary, laetrile may be beneficial when properly administered in a complete treatment program, but it is not the miracle cancer cure that its early proponents hoped it would be.

Side Effects and Toxicity

There have been reports of death and illness in children who took laetrile tablets accidentally. (1, 5) However, these incidents are not the result of therapeutic administration of the drug. There are also reports of muscular weakness and respiratory difficulties in patients taking laetrile. (20) Usually these side effects are seen in patients who6 self-administer excessively high doses or who directly consume apricot kernels, which can be quite toxic. (6)

Oral laetrile is converted to cyanide in the intestines by bacteria. Intravenous laetrile, in the most common form of administration, appears not to lead to the uncommon side effect of cyanide toxicity. (3)

On the whole, cyanide poisoning does not appear to be a major problem in laetrile therapy. Some patients have reported experiencing occasional episodes of toxemia, such as weakness, dizziness, nausea, vomiting, diarrhea, and fever. It is believed that these symptoms are related to the patient's impaired ability to dispose of the toxic products, as a result of tumor breakdown. In any case, no one should take laetrile without appropriate supervision and monitoring.


The Contreras Hospital in Tijuana, Mexico, has probably treated more cancer patients with laetrile than any other facility in the world. The director of Contreras Hospital, Harvard-educated Ernesto Contreras, Sr., has been administering the drug for over thirty years.

The Contreras laetrile protocol usually consists of administering 3 grams of laetrile intravenously daily, six days per week, for two to three weeks. The frequency of intravenous administration is gradually decreased, and oral tablets are used as the patient improves.

The Physician's Handbook of Vitamin B-17 Therapy gives an excellent summary of the various methods of administering laetrile. (12)

Laetrile is available in tablet form for maintenance therapy. Gauze-soaked solutions of laetrile or a water-soluble salve have been used to apply to open skin lesions. Laetrile solutions have been used as nighttime retention enemas, and are sometimes instilled directly into the intestines through a colostomy.

When treating cancer, most clinics administer laetrile intravenously. Injections directly into tumors are not advised. To achieve optimum concentration of laetrile in a tumor, laetrile should be injected into the artery above the tumor site. A table listing various tumor sites and the suggested arterial routes of administration is provided in the previously mentioned booklet. (12) It must be emphasized that intra-arterial administration should be done only in a hospital setting by qualified personnel.

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