Herbs and drugs: friends, enemies or allies against cancer?

The topic of interactions between oncologic drugs and natural products has been recently at the heart of two events organized by the Project Convivio at the Oncology Unit of the Hospital of Verona, with the participation of oncological out-patients, and of another event on nutrition and cancer held by EXPO-Milan in September 2015 at the Cereals and Tubers Cluster. In the case of Project Convivio, which envisages a series of activities on different topics developed under the guidance of experts, the patients themselves had asked for deepening the topic “herbs and drugs” and a look at the literature underlines that this matter is relevant not just abroad but in Italy too.
A study published in 2011 and based on almost 300 questionnaires submitted in the Piedmont Region shows that one oncologic patient over three uses herbs, aloe in particular, and one over five uses vitamin-based supplements;¹ whilst another Italian research in patients affected by chronic lymphocytic leukaemia reveals that 65% of patients uses complementary medicines and that green tea and aloe vera are the most used remedies.² Besides these numbers, the fact that strikes the most - and it is common to both studies - is that only few patients decide to disclose it to their oncologist, partially because the oncologist does not ask about it, but mostly because they are afraid to be discouraged in the use of herbs.
A fundamental distinction has to be made between the use of the herbs as anticancer or as integration to the treatments, even though it is not always easy to trace the borderline, because the thought that “it is not going to hurt” always prevails and there is always hope for a “miraculous” effect. Hope often fostered by newspapers articles with captivating and misleading titles, which presents these herbs (sometimes of common use) like possible cancer remedies, in the light of data coming from experimental research on their potential activity on cancer cell lines.
Thanks to the huge amplification provided by social networks and by word of mouth, then, questions arise among the patients. Are ginger or turmeric more effective than the more traditional onion and garlic? No, they are not effective but some studies show that ginger can effectively prevent nausea and vomit (post-surgery, induced by chemotherapy or anti-HIV drugs, in pregnancy) and in Italy a randomised double-blind study on 250 patients under cisplatin therapy is currently investigating a ginger extract against placebo, coordinated by the National Cancer Institute in Milan.³
Other studies showed that turmeric, well known for its anti-inflammatory and analgesic properties and used by traditional Chinese and Ayurveda Medicine, can reduce the side effects of chemotherapy drugs (for example the gastrointestinal ones) and improve the quality of life.⁴
Other preliminary evidences from case-control studies indicate that the intake of high quantities of garlic and onion could reduce the risk of stomach cancer, according to a meta-analysis published in 2015 by epidemiologists of the Mario Negri Institute of Milan.⁵
It is then possible to state that herbs and drugs can be friends or alleys, but beware: not everything that is natural is harmless too. Some species are toxic and within the same species some parts can be toxic whilst other are not. From borage, for example, the seeds can be used to extract the oil, whilst leaves and flowers contain hepatotoxic alkaloids, as tomato leaves do as well.
Lastly, can herbs interfere with the drugs the patient is taking? This is a largely unknown chapter, even though today we know that some herbs can increase or decrease the absorption and the process of transformation of drugs in our body. For example products largely used like hypericum and ginkgo are inductors of some isoenzymes of the cytochromes family and can increase the metabolism of anticancer drugs, diminishing their effectiveness, whilst grapefruit and garlic are inhibitors of the cytochromes and could have opposite consequences. All these are in vitro researches, but which ones do translate in clinically relevant interaction once taken? Up to date we have scarce information, but this does not mean that the problem is not relevant, only that is has not been studied in depth.
In regard to oncologic drugs, some in vitro data and clinical observations go in the same direction, like the CYP3A4 induction by hypericum and the correspondent decrease of blood levels of irinotecan and etoposide; in other cases in vitro data do not translate in clinical evidence.⁶ Since we are only starting to understand the interactions between oncologic drugs and herbal preparations now, a transparent and “brave” communication between patient and doctor is essential to obtain new information, but especially to avoid risks and damages.