Complementary and alternative medicines are used by one in two patients before and during cancer treatments, but they are frequently associated with drug-drug interactions, two studies at ESMO 2018 report.

Sarcoma patients show great openness to the use of complementary alternative medicines (CAMs) for supportive care, but they are poorly informed about safety issues and risk of interactions with anti-cancer drugs, according to one study.

By administering a structured survey over a 4-month period (1 January-30 April 2018), a team from the University Hospital Mannheim, Germany, investigated types and modes of use of non-conventional therapies among 152 outpatients with sarcoma, gastrointestinal stromal tumour (GIST) and desmoid tumours receiving care at a sarcoma centre. Researchers considered CAMs as a broad range of practices including supplementation of vitamins or minerals, Chinese or healing herbs, homeopathy, acupuncture, meditation, yoga, Tai Chi or changes in dietary habits, like switching to a ketogenic or vegan diet.

The main results showed that 51% of participants had used alternative methods in their lifetime, and 15% of them only during the disease, in parallel with cancer treatments. Also, cancer diagnosis showed to have sparked patients’ interest in CAMs in 44% of participants.

Patients were shown to be selective in their choices, as study supervisor Prof Peter Hohenberger said: “What we found is that vitamins and minerals are very popular but patients take them specifically rather than using multivitamin supplements. Vitamin D is in the leading position, followed by selenium plus zinc, vitamin C, and interest in vitamin B17 is emerging."

Despite the reported popularity of non-conventional therapies among patients, clear information on their side effects and potential interactions with other drugs is still lacking. In the survey, 60% of patients recognised that information they had on safety issues of CAMs was insufficient, although they showed low concern for any potential risks.

Hohenberger said: “When we looked at the sources of information on non-conventional practices, oncologists represented only 7%. In our study, patients mentioned repetitively that they were positively surprised about our interest in their use of CAMs.

“Patients mostly accessed information on complementary and alternative medicines on the Internet and other media (43%), friends (15%) and healing professionals (14%). In sharp contrast with this, when it came to finding information on side effects of cancer therapies or how to handle them, almost half of patients asked their oncologist.”

Drug-drug interactions (DDI) is a relevant but often neglected topic in medical oncology and because sarcomas are so rare (only 1% of all cancer cases) to improve medical knowledge and clinical research in this setting is still a challenge. At ESMO 2018, a retrospective review involving 202 sarcoma patients undergoing chemotherapy or tyrosine kinase inhibitors reported that 18% major drug-drug interactions occurred in the study period (from 2014 to 2018) and that medical reconciliation, making an inventory of all the medicines prescribed to and taken by patients is advised before cancer treatment initiation to prevent adverse effects or ineffective treatments.

Lead author Dr Audrey Bellesoeur of University Paris Descartes, France, said: “We know from previous research that one in three ambulatory cancer patients are susceptible to potential drug-drug interactions. A better understanding of these mechanisms is necessary today for a real personalised medicine.” In the study, DDI were more frequently observed with tyrosine kinase inhibitors while gemcitabine was associated with a significantly lower risk.

Bellesoeur added: “In our review, 29% of drug-drug interactions requiring pharmacist interventions were associated with complementary alternative medicines. Risks of interactions with non-conventional drugs are the same as for other co-medications: mainly increased toxicity and loss of efficacy of anti-cancer treatments. However, we often have less information on the composition of these products and their risk of toxicity or interaction when used in combination with other agents.”