Background: Newer personalized medicine including targeted therapies such as PARP inhibitors and CDK 4/6 inhibitors have shown to improve survival of breast and gynaecological cancer patients. However, efficacy outcomes may be hampered by treatment discontinuation due to targeted therapy-related adverse drug reactions or resistance. Studies suggest that add-on mistletoe (Viscum album L., VA) improves quality of life and ameliorates cytotoxic side effects of standard oncological therapy in cancer patients. The primary objective of this real-world data study was to determine the safety profile of targeted therapy in combination with add-on Helixor® VA therapy in breast and gynecological cancer patients. Methods: The present study is a real-world data study utilizing demographic and treatment data from the accredited national Network Oncology (NO) registry. The study has received ethics approval. The safety profile of targeted with or without Helixor® VA therapy as well as safety - associated variables were evaluated by univariate and adjusted multivariable regression analyses. Results: All stage breast or gynecological cancer patients (n = 242) were on average 54.5±14.2 years old. One hundred and sixty patients (66.1%) were in the control (CTRL, targeted therapy) and 82 patients (33.9%) in the combinational (COMB, targeted plus Helixor® VA therapy) group. The addition of Helixor® VA did not hamper the safety profile (χ2 = 0.107, p-value = 0.99) of targeted therapy. Furthermore, no adverse events and a trend towards an improved targeted therapy adherence were observed in the COMB group. Conclusions: The present study is the first of its kind showing the applicability of Helixor® VA in combination with targeted therapies. The results indicate that add-on Helixor® VA does not negatively alter the safety profile of targeted therapies in breast and gynaecological cancer patients.