Enterolactone-13C3 is the 13C-labeled Enterolactone (HY-108692). Enterolactone is a bioactive phenolic metabolite known as a mammalian lignan derived from dietary lignans. Enterolactone has estrogenic properties and anti-breast cancer activity[1]. Enterolactone is a radiosensitizer for human breast cancer cell lines through impaired DNA repair and increased apoptosis[2].