Unproven anticancer herbs

Phytomedicinals that have no proven value in the treatment of cancer but are nevertheless recommended for its treatment in the uncritical herbal literature are apricot pits, pau d’arco, and mistletoe.

Apricot pits Much less popular than they were a decade ago, the kernels of Prunus armeniaca L. of the family Rosaceae and their contained laetrile (up to 8 percent)—or, more accurately, amygdalin cyanide-containing principles— continue to be used occasionally as a cancer cure. An extensive clinical study begun by the National Cancer Institute in 1980 concluded that laetrile and natural products containing it were “ineffective as a treatment

for cancer.” 47 Apricot pits and laetrile are mentioned here only to call the reader’s attention to their lack of therapeutic value.

208 Tyler's herbs of choice: The therapeutic use of phytomedicinals Pau d’Arco

The bark of various South and Central American Tabebuia species (family Bignoniaceae) is sold under the name of pau d’arco, lapacho, or taheebo and used as a tea to treat various cancers. Presumably, it is purported to be effective because of its content of lapachol derivatives, yet lapachol itself was found to be too toxic for human use in clinical trials. 48,49 The effectiveness of pau d’arco in the treatment of cancer or any other condi- tion remains unproven, and the bark cannot be recommended.

Mistletoe Because of their reputation as toxic plants, neither European mistletoe, Viscum album L., nor American mistletoe, Phoradendron leucarpum (Raf.) Rev. & M. C. Johnst., is customarily available from commercial herb sup- ply houses in the United States. Both plants contain similar toxic poly- peptides known respectively as viscotoxins and phoratoxins, as well as lectins (glycoproteins) and many other physiologically active constituents, such as tyramine, histamine, and flavonoids. 50

European mistletoe has an ancient folkloric reputation as a treatment for hypertension, but in recent years much attention has been devoted to its potential antineoplastic effects when aqueous extracts of the plant are administered by subcutaneous injection. Between 1985 and 1990, some sixty

articles on this subject were published in the medical literature. 51 The most important active principles responsible for mistletoe’s cytotoxic and immu- nomodulating properties in the treatment of cancer appear to be the lectins.

Unfortunately, because of differences in processing methods and host tree sources, different preparations have different proportions of constituents; consequently, clinical trials using one preparation are not neces- sarily valid for other preparations. In reviewing the literature, Kleijnen and Knipschild found eleven controlled clinical trials that met predefined criteria for good methodology. None of the studies, however, employed a double-blind design. They found the average quality of the trials poor; the results, based mostly on survival time, were slightly in favor of mistle-

toe treatment. 52 At the present time, mistletoe extract and mistletoe lectins are being studied extensively, particularly in Germany, as immunostimulatory adjuncts to use along with standard modalities in the treatment of cancer. For example, one recent study found that in thirty-five patients suffering from malignant stage III/IV glioma, subcutaneous injections of mistletoe extract had an immunostimulatory effect that correlated with an improved quality of life as determined by a standard questionnaire. 53

Nevertheless, mistletoe’s effectiveness as an anticancer treatment is moot in the United States because suitable injectable preparations are unavailable there. In Europe, where they are available, their utility as

Chapter eleven: Performance and immune deficiencies 209 nonspecific palliative therapy for malignant tumors remains unproven

and is controversial. In addition, the German Commission E has declared that the use of the herb to treat hypertension requires substantiation. 54

Unproven anticancer herbs