ESR1 and breast cancer: The patient was a 53 year old Caucasian woman, without any previous major medical problems, who was recently diagnosed with synchronous bilateral breast cancers and who underwent a right modified radical mastectomy and a left total mastectomy and left axillary sentinel lymph node biopsy for a pT2, pN1, estrogen receptor positive, progesterone receptor positive, HER-2/neu negative invasive lobular carcinoma of the right breast and a pT1b, pN0, estrogen receptor positive, progesterone receptor positive, HER-2/neu negative invasive ductal carcinoma of the left breast, respectively.