ESR1 and breast cancer: Several previous studies reported MPD expresses ER only in 10% of cases.17, 18 Similarly, the ER‐positive rate in extramammary Paget's disease(EMPD) was demonstrated at the range of 4%‐19%.18, 19 On the other hand, both MPD and EMPD had a relatively high rate of androgen receptor (AR) expression and antiandrogen therapy was an effective treatment for EMPD.19, 20 The different expression pattern of steroid hormone receptors suggests that maybe ER expression is not so important in MPD as in other types of breast cancer, which may be one explanation for our surprised finding.