Treatment of metastatic extramammary Paget's disease associated with adnexal adenocarcinoma, with anti-HER2 drugs based on genomic alteration ERBB2 S310F

Extramammary Paget’s disease is a rare intraepithelial malignant condition affecting the apocrine gland-bearing skin. In this case, a genomic alteration, ERBB2 S310F mutation, was discovered. The ERBB2 S310F mutation seems to be a transforming mutation that should be targeted with anti-HER2 drugs. Genomic tests are justified in rare tumors.