A 46-year-old woman with medical history significant for BRCA2 gene mutation (1222delA), estrogen receptor positive (ER+) ductal carcinoma in situ (DCIS) of the left breast status-post total mastectomy and breast implantation, and multiple sclerosis on natalizumab presented to her dermatologist with a new lesion on her scalp for 6 months (Fig 1, A). Here, ESR1 is linked to ductal breast carcinoma in situ.