Background: Approximately half of all patients with cancer use at least one method of complementary medicine during or after tumor treatment. The substances most commonly taken are micronutrients, food supplements, and plant extracts.
Methods: This guideline is based on pertinent articles retrieved by a systematic search in the Medline, Cochrane Library, Embase, PsycInfo, and Cinahl databases.
Results: The evidence is offen scant for any effect of a complementary method on patient-relevant endpoints such as relief of disease symptoms, reduction of treatment side effects, or prolonged survival. Micronutrients are available in different compositions, and their dosages vary. In most studies on the use of vitamins and trace elements by cancer patients, the blood level of the substance in question was not measured before its administration, so that it remains unknown whether a deficiency was present. For this reason, no well-founded conclusion on the effects of these substances can be drawn, and their use cannot be recommended in most cases. On the other hand, there is high-level evidence supporting physical exercise by cancer patients during and after their treatment. For patients with any type of cancer, mortality is lower among those who perform more physical exercise, whether before or after they receive the diagnosis of cancer (exercise before diagnosis, hazard ratio [HR] 0.82, 95% confidence interval [CI] [0.79; 0.86]; exercise after diagnosis, HR 0.63, 95% CI [0.53; 0.75]). Physical exercise during and after treatment for cancer should, therefore, be recommended to all cancer patients.
Conclusion: The inherent positive attribute of complementary medicine is patient empowerment: it enables patients to help themselves in an active way even while undergoing cancer treatment, as well as afterward. To avoid risks to health, patients should be instructed about unsafe methods, asked repeatedly about their use of complementary medicine, and informed specifically about potential interactions between such interventions and their cancer treatment.