The websites and other resources your patients find on the Internet may downplay or ignore clinical evidence that herbal supplements may promote tumor growth or impair the effectiveness of established cancer treatments.
The websites and other resources your patients find on the Internet may not only be providing false or unsubstantiated information regarding the cancer-fighting benefits of untested herbal supplements, they may also be downplaying or ignoring clinical evidence that these supplements may promote tumor growth or impair the effectiveness of established cancer treatments.
The popularity of a variety of so-called “complementary” or “alternative” medical strategies employed by the public has been well documented. It is also increasingly appreciated that cancer patients pursue a wide variety of treatment approaches outside the medical mainstream for dealing with symptoms of cancer, side effects of treatment, and potentially intense emotions like anxiety and fear that follow a cancer diagnosis. Both the hypothesized benefits and potential risks associated with a wide spectrum of such strategies have been extensively discussed in the medical and lay literature.
One specific form of alternative medicine that should be of particular concern to oncologists and other cancer health professionals is the increasing prevalence of individuals with cancer who elect to self-administer or receive from a practitioner a variety of herbs or other untested “medications” (eg, high-dose vitamin C). These approaches may be utilized to directly treat the cancer (eg, through “augmentation” of natural immunity) or prevent or ameliorate the toxic effects of standard anti-neoplastic drugs.
Although the existence of alternative cancer treatments for which there are unsubstantiated (and subsequently disproved) claims of direct benefits is certainly not a new phenomena (eg, laetrile), what is of increasing concern is objective evidence that a number of these essentially unregulated supplements and pharmaceuticals may actually cause harm. In fact, there is a growing body of pre-clinical and clinical data that indicates that when some of these unproven but biologically active agents are taken by an individual (with or without cancer), serious and completely unanticipated consequences may result (see sidebar).
Several disquieting evaluations of such products reported in the recently published medical literature emphasize this point. The observation of two men who developed aggressive prostate cancer shortly after taking the same herbal dietary supplement designed to “solve health and aging issues” led to an examination of the effect of the product on cancer cell growth. Tested against established prostate cancer cell lines, the investigators found this preparation to be “a more potent dose-dependent stimulator of cancer cell growth than testosterone both in androgen receptor-negative and receptor-positive cell lines.”
In another report, a dietary supplement “advertised to ameliorate female sexual dysfunction” was demonstrated in an in vivo model to result in the growth of estrogen-dependent breast cancers. Finally, two laboratory-based studies have revealed that the supplement genistein, employed to ameliorate post-menopausal symptoms, may impair the anti-neoplastic activity of both tamoxifen and letrozole.
It must be emphasized that these are only a few examples of tested products. How many other alternative medications are being taken by an unsuspecting public that may result in serious consequences related to cancer progression or interfere with the effectiveness of established anti-neoplastic therapy?
High-concentrations of Vitamin C
Whereas the lack of evidence for the benefit of alternative medications is of legitimate concern, perhaps the greatest potential danger of such approaches is the risk that a particular product may actually directly prevent an established anti-neoplastic agent from killing a viable tumor.
Recently reported experimental data regarding the ability of vitamin C, in a dose-dependent manner, to protect cancer cells from the cytotoxic effects associated with a variety of important and widely utilized anti-cancer drugs (doxorubicin, cisplatin, vincristine, methotrexate, imatinib) have rather profoundly changed this discussion from an abstract concern to a potentially serious health hazard. The fact that this negative effect of vitamin C was so broad-based suggests that the protective influence relates to a fundamental mechanism of tumor cell killing and may be operative when essentially any anti-neoplastic agent is administered to treat a human cancer.
Over the years, multiple unsubstantiated claims have been advanced for the benefits of vitamin C as a cancer treatment. Although anecdotal reports and preclinical data provide a theoretical rationale for further exploration of this agent in well-designed and appropriately conducted prospective clinical trials, the question remains: how many cancer patients are currently routinely receiving this agent (and potentially at high concentrations when administered intravenously) in combination with established therapy and may actually be harmed by this approach to disease management?
The increasing importance of the Internet as a resource for cancer treatment-related information is well recognized. Considering the relevance of the potential toxicity of alternative medications in the cancer patient population, I thought it would be interesting to survey the extent of discussion of this topic among Internet sites dealing with the general topic of alternative medical treatment of cancer.
To begin a high-level examination of this issue, I conducted two brief searches (utilizing Google as the search engine) on December 28, 2008 employing the search phrases “herbal treatment of cancer” and “vitamin C treatment of cancer” (see table). The intent of this exercise was to determine the percentage of the initial 25 sites examined with each search phrase that included either a general comment regarding the potential toxicity of a given alternative treatment, or a detailed discussion of specific risks (in the case of vitamin C, this would include the data related to the experimental evidence noted above).
The initial search included the websites of a number of academic health centers. I decided to exclude these sites from this examination, since my overall aim was to explore the type of information being provided to the public (and cancer patients) that did not come from traditional medical sources (even if these traditional medical sources are now quite appropriately and often quite effectively employing the Internet as a strategy to communicate with the public).
Discussion of Potential Alternative Medicine Management-related Toxicity within the Initial 25 Internet Sites Identified by Each of Two Specific Search Strategies
Review of the data from this brief survey leads to several conclusions. The majority of the initial 25 non-academic medical center websites found by employing either search phrase did not include any statement regarding the potential toxicity of either herbal treatments or vitamin C treatment of cancer.
However, there were several very notable exceptions, including the website Quackwatch, which appeared in the top 25 listings of both searches and provided extensive (and easily readable) information regarding the topics. It is also relevant to note that several of the listed sites offered links to the published peer-reviewed papers in this area or cited relevant news reports describing study findings that raised concerns regarding the potential for adverse effects associated with non-approved agents.
Dangerous claims vs. objective data
Although the absence of oversight of the information on the Internet permits widespread dissemination of unsubstantiated and potentially dangerous claims related to approaches to prevent or treat cancer. The Internet is a powerful method of communication that can also be employed by organizations and individuals who desire to provide objective data and educate the public regarding the meaning and importance of scientific evidence in the selection of appropriate cancer management.
What approach do you take when counseling patients who are interested in trying herbs, supplements, and other forms of alternative medicine? Do you talk to your patients about the vast amount of misinformation available online regarding the supposed benefits of alternative cancer treatments?
Dr. Markman is the Physician Editor-in-Chief of Oncology Net Guide, and the VP of Clinical Research at MD Anderson Cancer Center, Houston, TX.
Clinical studies outlining the potential harmful effects of herbal and dietary supplements when used by patients undergoing treatment for cancer
Dietary Genistein Negates the Inhibitory Effect of Letrozole on the Growth of Aromatase-expressing Estrogen-dependent Human Breast Cancer Cells (MCF-7Ca) in vivo
Dietary Genistein Negates the Inhibitory Effect of Tamoxifen on Growth of Estrogen-dependent Human Breast Cancer (MCF-7) Cells Implanted in Athymic Mice
A Dietary Supplement for Female Sexual Dysfunction, Avlimil, Stimulates the Growth of Estrogen-dependent Breast Tumors (MCF-7) Implanted in Ovariectomized Athymic Nude Mice
Dietary Supplement Possibly Associated with Prostate Cancer Progression
Vitamin C Antagonizes the Cytotoxic Effects of Antineoplastic Drugs