Background: Traditional medicine is inspiring in drug development research. Epilobium parviflorum extracts have shown promising therapeutic effects on prostate cancer cells. The similarities between breast and prostate cancers at molecular and metabolic levels prompted us to explore its effects on human breast cancer.
Methods: The root, aerial parts and flowers of the plant were, collected and dried separately at ambient temperature and away from direct sunlight. The aquatic and methanolic extracts of each part was prepared. The effect of each extract on the growth of MCF-7 breast carcinoma cells and HEK293 normal cell line was evaluated, using MTT assay. Each experiment was repeated at least three times independently. The IC50 values for each treatment time point were analyzed, using ANOVA at P<0.05.
Results: While none of the extracts had considerable toxicity on normal HEK293 cells, some of them showed varying levels of toxicity on the MCF-7 cells. The methanolic extracts were more cytotoxic than the aqueous counterpart. The roots’ methanolic extract showed the strongest cytotoxicity on the MCF-7 cells in a dose and exposure time dependent manner. The IC50 after 48 hours of treatment was determined at 73µg/ml.  
Conclusion: This study is the first to demonstrate that Epilobium parviflorum had a strong growth inhibiting property on MCF-7 cell line, as a potential model to treat human breast cancer cells. The most cytotoxic effect was noted for the methanolic root extract. Determination of the effective biochemical constituents of the extract against cancer cells is the focus of our future research.