ESR1 and breast cancer: In the case of breast cancer, while anacardic acids (1a–d) are active cytotoxic agents against BT-20 breast carcinoma cells [41], anacardic acid 6b (C24:1 ω5) from geraniums (pelargonium × hortorum) inhibits the proliferation of estrogen receptor α-expressing breast cancer cell lines, estrogen response element interaction, and the transcription of estrogen response target genes [42].