A Current Assessment of the Use of Complementary Medicine in German Cancer Patients: The CONKO 022 Investigation Open Access

Complementary and alternative medicine (CAM) includes the following five categories: mind-body therapies, biologically based practices, manipulative and body-based practices, energy therapies, and whole medical systems [1‒4]. Alternative medicine uses nonevidence-based therapies as substitutes for conventional medical treatments. In contrast, complementary medicine supplements standard care and is used alongside conventional treatments [5]. Integrative medicine combines conventional and complementary approaches in an evidence-based manner, emphasizing a holistic treatment strategy tailored to individual patient needs [6].

Previous studies found approximately half of oncology patients nowadays using CAM therapies as general interest in CAM has risen significantly over recent decades [7]. In particular, women, younger patients, those with higher educational degrees, as well as patients diagnosed with breast cancer have reported use of CAM more often [8, 9]. Patients often seek CAM to enhance recovery post-therapy, alleviate side effects of conventional treatments, support their immune system, or improve overall physical and mental well-being. Additionally, some patients are motivated by the desire to actively participate in their cancer treatment and CAM can be valuable adjuncts to conventional therapies [10‒12]. However, biologically based CAM therapies, such as supplements and phytotherapy, can pose significant risks due to potential drug interactions. A recent study reported 51% of cancer outpatients at risk for CAM-related drug interactions, highlighting a substantial safety concern [13]. Earlier studies have reported even higher risks, with up to 65% and 85% of patients potentially affected by drug interactions from CAM therapies [14, 15]. However, comprehensive German data on application and communication between among adult cancer patients and oncologists regarding CAM are scarce. To support safe CAM use in Germany, resources such as the S3 guideline on CAM in oncology, the Memorial Sloan Kettering Cancer Center (MSKCC) database, and the Kompetenznetz Komplementärmedizin in der Onkologie e.V. (KOKON) have been established. These resources provide evidence-based information for healthcare professionals and accessible information for patients [16‒19]. Research indicates that while CAM can offer benefits, many treatments lack robust in vivo evidence [20].

The aim of this study was to assess CAM practices among adult oncology patients in Germany both pre- and post-diagnosis, thereby expanding the currently limited data on this issue. We also investigated communication aspects between patients and oncologists regarding the use of CAM as well as potential risks of drug interactions. Furthermore, we analyzed the frequency of application of particular CAM practices.

This study was approved by the Charité – Universitätsmedizin Berlin Ethical Review Committee (file reference: EA1/158/22) and was performed in accordance with the Declaration of Helsinki and the guidelines of Good Clinical Practice. The Ethics Committee has agreed that in this non-interventional study, sole verbal consent from the patients is sufficient. Patients did not receive financial compensation for their participation.

This cross-sectional study was conducted between September of 2022 and June of 2023. Patients were recruited after having been approached by their attending physician or assistant medical students either at the Department of Hematology, Oncology, and Tumor Immunology of Charité – Universitätsmedizin Berlin, Germany, or at a cancer support group in Krefeld, Germany. In addition, multiple postings at the outpatient department provided further information on the study.

Inclusion criteria were sufficient German language capability, at least 18 years of age, and an oncological or hematological diagnosis. Also, patients’ overall cognition must have allowed for informed consent regarding their study participation.

Patients were surveyed using a comprehensive questionnaire consisting of five parts. First, sociodemographic parameters such as age, sex, and educational degree were assessed. Second, patients were asked about diagnosis-related details. Third, the most commonly used CAM practices were listed and patients were asked about application details. This list consisted of 18 CAM practices and patients were asked to add any other CAM practices used. Fourth, communicational aspects of CAM use between patients and their attending physician were assessed. Questions included whether patients informed their oncologists about their use of CAM as well as questions whether oncologists gave medical advice regarding potential risks. Fifth, patients were asked to evaluate their current quality of life using numbers between 0 and 100 with higher numbers indicating better quality of life. Patients answered all questions discretely and without time limit and were offered to record their answers using paper questionnaires or the web application Research Electronic Data Capture System (REDCap) [21, 22]. Paper questionnaires were entered into the digital REDCap database subsequently.

A descriptive analysis of sociodemographic and diagnosis-related parameters as well as of data regarding patients’ quality of life was performed using means, median, standard deviation, frequencies, and percentages. Differences in application of CAM practices depending on sociodemographic parameters, quality of life, or application timing were analyzed using the Kruskal-Wallis test, one-factor ANOVA, and post hoc analysis. CAM application before and after cancer diagnosis was compared and diagnoses as well as other clinical parameters were grouped for statistical analysis. Data analysis was performed using SPSS Statistics version 28 (Chicago, IL, USA).

The sociodemographic and clinical parameters of all participating patients (n = 154) are displayed in Table 1. The median age was 59 years.

Out of all 154 patients, 136 (88.3%) reported to have used CAM practices either before or after their cancer diagnosis or both. Patients using CAM practices pre-diagnosis or pre- and post-diagnosis most frequently used massage therapy (n = 68), dietary supplements (n = 54), yoga (n = 47), and acupuncture (n = 46). Those who commenced using CAM practices only after their diagnosis most frequently reported application of dietary supplements (n = 44), massage therapy (n = 25), meditation (n = 25), and homeopathy (n = 24) (shown in Fig. 1).

In total, 62.3% of patients reported to have commenced at least one CAM practice after their diagnosis, while 10.4% of patients had not used any CAM practices until post-diagnosis. However, 77.9% of all patients said to have used at least one CAM practice already pre-diagnosis with 26.0% of patients reporting to have used CAM practices solely before their cancer diagnosis. In-depth analysis of CAM use showed significant differences between sexes. Female cancer patients used CAM practices more frequently than male patients did. This was especially true regarding post-diagnosis CAM use (p = 0.022) (shown in Fig. 2). Also, the median of patients had received their diagnosis 12.5 months prior to our study. Those with earlier diagnoses showed a tendency toward higher frequency of CAM use (p = 0.17).

Sex differences were also found regarding the use of cannabis and yoga. Cannabis was used by both 5 female and male patients pre-diagnosis and nine female versus zero male patients post-diagnosis (p = 0.034). In case of yoga, female patients also reported post-diagnosis use more often than male patients did, although this difference did not reach significance threshold (p = 0.155). Besides sex differences, age did not show significantly different frequencies of application (p = 0.559). Same held true for comparisons between subgroups of educational levels (p = 0.186). However, massage therapy showed a tendency of more frequent use among patients with higher educational levels (p = 0.133). Analysis of patients grouped by their net income did not show significant differences. Neither comparisons between below- versus above-average net income (p = 0.491) nor more detailed comparisons between multiple income groups (p = 0.746) indicated relevant differences in CAM use. Regarding groups of cancer diagnoses, patients suffering from breast cancer reported post-diagnosis CAM use significantly more often than patients suffering from other malignancies (p = 0.004). Specifically, this contrast showed the strongest between breast cancer patients and lymphoma patients (p < 0.001).

Patients’ answers to their personal health-related quality of life showed a median score of 60.5 points out of 100 ranging from 13 to 100. Statistical comparisons between quality of life and CAM use showed a mean score of 66.3 points among patients without CAM use, while patients with post-diagnosis CAM use reported scores of 55.7 points. Patients reporting only pre-diagnosis CAM use reached mean scores of 59.8 points. These differences did not reach statistical significance (p = 0.148) (shown in Fig. 3).

In total, 60.8% of all patients using CAM pre- or post-diagnosis reported to have informed their attending physician about their use of CAM, while 39.2% did not share this information with their oncologist. Regarding reasons for noncommunication among the latter group, the majority of patients (74.5%) explained that they regarded their use of CAM as irrelevant to the medical treatment they received. Another 15.7% of patients stated there was a lack of time during the interaction with their physician to speak about their use of CAM and 9.8% of patients assumed a potential negative opinion of their physician regarding their use of CAM. However, among patients using CAM only pre-diagnosis, 52.8% notified their attending physician. In contrast, 66.7% of post-diagnosis CAM using patients did so. Also, patients having used only substance-related CAM methods (e.g., probiotics, phytotherapy, dietary supplements, or cannabis) notified their attending physician more often (60.4%) than patients having used only non-substance-related CAM methods such as yoga or massage therapy (44.6%). Regarding physicians’ communication, 63.7% of all patients reported to have not received any information about CAM use – neither positive aspects nor potential risks. However, among patients who used CAM post-diagnosis, 46.6% stated they were informed on potential drug interactions with CAM practices.

Overall, 18 patients shared information on financial aspects of CAM use. Answers ranged from EUR 20 to EUR 300 per month with patients using CAM pre-diagnosis reporting monthly costs of EUR 20 to EUR 30 and patients using CAM post-diagnosis spending between EUR 20 and EUR 300.

The main findings of our study highlighted the frequency and relevance of CAM practices for German cancer patients. This is underscored by almost 2 thirds of all patients having commenced use of at least one CAM practice after receiving their cancer diagnosis and even over three-fourths of all patients using at least one CAM practice already before their diagnosis. The highest prevalence of CAM use was found among women and breast cancer patients, while other sociodemographic parameters such as age, net income, or level of education did not show significant differences. However, all breast cancer patients in our study were female. Hence, breast cancer patients may have reported use of CAM more often rather due to their sex than due to their diagnosis. The overall most frequently used CAM practice was dietary supplements. Pre-diagnosis, patients also favored massage therapy, yoga, and acupuncture. Besides massage therapy, meditation and homeopathy appeared as most popular post-diagnosis. Interestingly, CAM methods of higher physical intensity (e.g., yoga) were used more frequently pre-diagnosis, while practices requiring lower physical activity (e.g., meditation) were preferred post-diagnosis. Besides, the frequent intake of dietary supplements may entail potential interactions with the patients’ oncological treatment. However, almost 40% of patients did not inform their physician about their use of CAM and over 60% of patients did not receive any medical advice on potential drug interactions from their physician.

Regarding our study results in the context of current literature, use of CAM appears to be frequent yet insufficiently studied among German cancer patients. While over 85% of patients reported use of CAM in our study, previous studies found rates of CAM use in the range of 60% among German cancer patients (without providing further information on the exact timing of use) to 95% among American cancer patients undergoing radiation [11, 23]. In line with our findings, dietary supplements were also reported as the most frequently used CAM method [11]. Other studies were able to identify associations between frequent use of CAM with certain sociodemographic or clinical characteristics. Some detected women, breast cancer patients, younger patients, or those with higher educational degrees to be more likely to use CAM, while a different study only found younger age to be a predictive factor of CAM use [8, 13]. As our study found women and breast cancer patients using CAM significantly more often, literature appears to be currently inconsistent regarding distinct patient parameters correlating with the use of CAM. Breast cancer patients’ higher tendency toward CAM use may be due to typically high survival rates and life expectancy, making CAM practices potentially more interesting and relevant for personal well-being. Further research on CAM use depending on patients’ prognoses and time since diagnosis is needed.

Although information on CAM can be found in many places, physicians are reckoned to be the best source of information on CAM in Germany [24‒26]. Interestingly, our study found over 60% of patients reporting to have notified their attending physician about their use of CAM. Previous data on the disclosure of CAM to physicians are heterogeneous yet lower with rates ranging from 12.1% to over 50% [23, 27, 28]. Potentially, patients participating in our study were generally interested in CAM practices and thus more communicative about such therapies, leading to higher disclosure rates. However, a standardized questionnaire on CAM use at the first medical consultation may lead to a more patient-tailored treatment focus, improved patient safety, and better therapy outcomes.

The design of our study allowed for a general analysis of CAM use among cancer patients in German adult cancer patients. However, limitations of our study involved the heterogeneous study population as well as potential selection or recall bias. Identification of predictive factors for CAM use was limited due to the heterogeneous study population including patients diagnosed with various malignancies as well as different stages of therapy. In addition, patients mostly filled out the questionnaire during their time of waiting at the outpatient department, which may have led to a biased recruitment toward patients with a general interest in CAM. This may have also been true regarding the recruitment of patients at a cancer support group. Also, since this study provides a structured overview of the frequency of CAM, single practices – such as interval of massages or specific substances like mistletoe, which is commonly used by cancer patients in Germany – were not assessed in detail. Instead, these were categorized into larger groups – such as phytotherapy – rather than assessed separately. In addition to studies like this which provide an overview of the topic, further research is essential to focus on the details of each relevant CAM practice. Moreover, the use of the most commonly prescribed medicinal herbs, mistletoe therapy, appears to be quite heterogeneous in Germany and therefore warrants more thorough investigation in the future [29, 30]. For patients whose used CAM practices in the past, a recall bias could not be ruled out.

This study provides a general overview of the use of CAM among German adult cancer patients. CAM use appeared to be of great importance to patients with user rates of over 85%. Dietary supplements were named as the most frequent CAM practice. Women and breast cancer patients reported CAM use significantly more often than other patients did. The financial burden on patients ranged between EUR 20 and EUR 300 per month with higher amounts spent post-diagnosis. Disclosure rates on CAM use between patients and their attending oncologists was higher than in other studies. Yet, better education as well as heightened awareness of healthcare providers regarding CAM practices is needed to help mitigate potential drug interactions as well as support patients’ desire to actively engage in their treatment. Further research is needed to study the application and impact of specific CAM substances and practices like mistletoe therapy as well as differences regarding dosages, timing of application, and duration more in details.

This study was approved by the Charité – Universitätsmedizin Berlin Ethical Review Committee (file reference: EA1/158/22). Patients were asked for their consent to participate in the study prior to the examination. Since no personal data were recorded, consent remained orally only.

S.S. reports advisory roles unrelated to this work from Amgen, AstraZeneca, 548 Bayer, BMS, Daiichi Sankyo, ESAI, Janssen, Lilly, Merck KGaA, MSD, Pierre-Fabre, Roche, Sanofi, 549 Servier, Taiho, and Takeda and has received research funding from Merck KGaA, Pierre-Fabre, Servier, and 550 Roche. All other authors declare no conflicts of interest.

This study was not supported by any sponsor or funder.

Conceptualization, supervision, and project administration: L.U.S. and U.P.; methodology: L.U.S., U.P., and T.B.; software: T.B., L.U.S., J.A., and L.B.; validation: L.U.S., U.P., M.O., and T.B.; formal analysis and investigation: J.A., L.B., and T.B.; resources: U.P., S.S., and M.O.; data curation: L.U.S. and T.B.; writing – original draft preparation and visualization: T.B., and writing – review and editing: L.U.S., U.P., M.O., and S.S. All authors have read and agreed to the published version of the manuscript.

The raw data supporting the conclusions of this article as well as the questionnaire ware not publicly available due to privacy reasons but will be made available by the corresponding author upon request.