Samenvatting

Background: Immune-related adverse drug reactions (ADRs) to immunotherapy agents have been associated with beneficial clinical outcomes in oncology. Viscum album L. (VA, European mistletoe) is frequently used as an immunomodulatory agent alongside conventional cancer treatment in Europe. VA has been associated with improved quality of life and a reduction in chemotherapy-related ADRs. Beneficial effects of VA are believed to be related to its immunomodulatory properties. Current guidelines recommend commencing with a low dose and increasing slowly overtime, however, off-label prescribing of high initial doses is common.
Purpose: We investigated ADR profiles related to subcutaneous VA therapy commencing with low, recommended doses versus higher than recommended doses.
Study Design: Retrospective cohort study.
Methods: Medical records of 1361 cancer patients treated between 2003 and 2013 were assessed. Patients were divided into two groups based on whether the dose of their first VA injection adhered to current guidelines. Patient characteristics and suspected VA-related ADRs were compared between dose groups.
Results: Of 1361 cancer patients, 516 (38%) started with a recommended, low dose of VA(≤0.02 mg) and 845 (62%) started with a higher dose(>0.02 mg). Groups did not differ by age or gender, but significant differences were observed for type (p < 0.001) and stage of cancer (p = 0.05). Starting with a high dose of VA was significantly associated with a higher incidence of VA-related ADRs compared to starting with a low dose (20.7% versus 0.8%, p < 0.001). Adjusting for age, gender, tumour type and stage of disease, produced an odds ratio of 37.5 (95% CI = 15.7–122.8, p < .001). Almost all ADRs, irrespective of the initial VA dose, were of mild or moderate intensity. Most ADRs were immune-related, general disorders and administration site conditions, many of which are desired reactions, such as pyrexia and local reactions. Overall, no serious ADRs occurred.
Conclusions: Starting VA therapy with a higher than recommended dose was associated with a high frequency of ADRs, however, nearly all ADRs were expected, of mild to moderate intensity and most were desired reactions. Future research is necessary to investigate whether higher incidences of immune-related events are indicators of beneficial immunomodulation and better clinical outcomes.