Safety and efficacy of the long-term adjuvant treatment of primary intermediate- to high-risk malignant melanoma (UICC/AJCC stage II and III) with a standardized fermented European mistletoe (Viscum album L.) extract. Results from a multicenter, comparative, epidemiological cohort study in Germany and Switzerland.

BACKGROUND: Mistletoe therapy is the most frequently used complementary treatment in cancer patients in Germany and Switzerland. However, its safety and efficacy were controversially discussed, also in case of malignant melanoma (MM).
OBJECTIVES: The present study should evaluate the therapeutic safety and efficacy of a long-term therapy with a standardized fermented European mistletoe (Viscum album L.) extract Iscador (FME) during post-surgical aftercare of primary intermediate to high-risk MM (UICC/AJCC stage II-III) patients and compare it with an untreated parallel control group from the same cohort.
METHODS: The study was designed as a multicenter, comparative, retrolective, epidemiological cohort study with parallel groups, carried out according to the guidelines of Good Epidemiological Practice (GEP). All patients suffered from surgically treated and histopathologically confirmed primary MM in UICC/AJCC stage II-III without distant metastases. In the study group, FME was administered subcutaneously 2-3 times weekly for at least three months, while the untreated control group was merely observed ("watchful waiting"). In both groups some patients also received radio-, chemo-, and/or immunotherapy. The patients were followed until the last visit or until death. Unselected, chronologically ordered, and standardized anonymous data from medical records that satisfied the predefined eligibility criteria were included for the "per protocol" analysis. Safety was assessed by the number of patients with FME-associated adverse drug reactions (ADRs) and by the search for tumor enhancement. The primary endpoint of efficacy was the adjusted tumor-related survival. Secondary end-points were the overall-, the disease-free- and the brain metastasis-free survival. The survival results were analyzed after adjustment for baseline imbalances, treatment regimens and other potential confounders by the Cox proportional hazard regression method.
RESULTS: 686 eligible patients (329 FME vs. 357 controls) from 35 centers were observed for a median aftercare of 81 vs. 52 months. The median FME therapy duration was 30 months. At baseline, both groups were comparable concerning demography, tumor history and risk factors for progression. Additional adjuvant chemotherapy was more frequent in the study group, while immunotherapy was more frequent in the control group. Eleven patients (3.3 %) developed systemic ADRs attributed to the FME-treatment, and 42 patients (12.8 %) developed local ADRs, with mild to intermediate (WHO/CTC grade 1-2) ADR severity and spontaneous resolution in most cases. In six patients the ADRs resulted in therapy termination. Life-threatening ADRs, ADR-related mortality or tumor enhancement were not observed. On the contrary, the incidence rate of lung metastases and the adjusted hazard ratio for brain metastases were significantly lower in the FME group. In the course of the study and during aftercare a total of 212 (30.9 %) patients relapsed or progressed, and 107 (15.6 %) died. A significantly longer tumor-related survival was found in the FME group when compared with the untreated controls (unadjusted tumor-related mortality rate 8.9 % vs. 10.7 %, Kaplan-Meier estimate, Log-rank test, p = 0.017), which was confirmed after adjusting for potential confounders by the tumor-related mortality hazard ratio estimate HR (95 % confidence intervals) = 0.41 (0.23-0.71), p = 0.002. The adjusted HR results of the overall survival, disease-free survival, and the brain metastases-free survival were also significantly superior in the FME group.
CONCLUSION: The long-term FME treatment in patients with primary intermediate to high-risk MM appears safe. Tumor enhancement was not observed. When compared with an untreated parallel control group from the same cohort, the results of the FME treatment suggested a significant survival benefit in primary stage II-III MM patients. These results on survival warrant reconfirmation in a prospective randomized clinical trial with optimized study design and treatment conditions.