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Complementary medicine (CM) is used widely in cancer patients, mostly in palliative treatment regimens or during chemotherapy. In contrast, the use of CM during curative Radiotherapy (RT) is less frequent. The aim of this study was to evaluate the influence of CM with regard to toxicity and recurrence during postoperative radiotherapy for breast cancer.

Between 2010 and 2013 all patients intended for adjuvant radiotherapy for breast cancer received a questionnaire concerning the use of CAM e. g. Vitamins, trace elements, enzymes, natural herbs etc. (yes/no) and if yes what kind. At the time Radiotherapy was applied with 50.4 Gy to the whole breast and a Boost of 10.8 Gy in 6.5 weeks. 6 weeks after radiotherapy the side effects were analyzed according RTOG grading. Follow up for progression rates was done yearly until January 2018. To determine whether there is a significant difference between the expected frequencies and the observed frequencies, a chi-squared test was used. All events were collected until January 2018.

A total number of 879 patients with breast cancer completed the questionnaire, 641/879 (73 %) patients did not take any complementary medicine (non CAM) and 238/879 (27 %) patients took CAM. There were almost 40 different products mentioned. 137/238 (57.6 %) patients took one CAM product, 86/238 (36.1 %) two, and 15/238 (6.3 %) more than two CAM products. The most common products were magnesium (Mg) in 71/238 (30 %) patients followed by selenium in 38/238 patients (16 %).

The RT side effects (Dermatitis RTOG grade 0, I, II, III/IV) 6 weeks after completion of RT were as follows: in the non CAM group 53 % grade 0, 41 % grade I, and 6 % grade II, 0 % grade III/IV. And in the CAM group 54 %, 38 %, 8 %, and 0.4 % respectively. The corresponding side effects for the group taking magnesium were 51 % 42 %, 6 % and 1 % and for the selenium group 47 %, 47 %, 5 % and 0 %). There was no significant difference in side effects between the non CAM and CAM patients, respectively magnesium and selenium.

The sum of all registered disease progression (0 years – 5 years) were in the non CAM group 6.4 %, in the CAM group 6.3 %, in the magnesium group 5.6 % and in the selenium group 7.9 %, no significant difference could be detected between all groups.

In this cohort, 27 % of patients used CAM during adjuvant radiotherapy of breast cancer. The most commonly used product is magnesium followed by selenium. A significant influence of CAM on subacute RT side effects or disease progression could not be identified. However, the higher rate of local and systemic failure in the selenium group appears remarkable. Therefore, this analysis will be further continued with a higher number of patients.