Abstract
BACKGROUND: Extramammary Paget's disease (EMPD) is a rare intraepithelial adenocarcinoma that occurs in the genitals, axilla, and anus, where apocrine sweat glands are abundant. This disease is mainly characterized by localized lesions and rare distant metastasis. Scrotal Paget's disease is a rare type of EMPD, and there is no standard treatment for metastatic EMPD. CASE DESCRIPTION: Here, we reported the genetic results of a patient with a PIK3CA gene mutation in scrotal Paget's disease who developed multiple metastases to the lymph nodes, liver, and bones during adjuvant radiotherapy, as well as the results of treatment with a PIK3CA inhibitor. The latest advances in this field were also summarized. The treatment response was evaluated as stable disease (SD) after 6 courses of docetaxel plus tegafur (DS regimen) chemotherapy. Then, a second-line treatment, a PIK3CA inhibitor, WX390, was administered with tolerable toxicity. There was a treatment-induced increase in blood glucose level during treatment, and insulin was administrated with good control. The progression-free survival (PFS) was 3.9 months and the overall survival (OS) was 16 months. CONCLUSIONS: PIK3CA is a commonly mutated gene in EMPD. To the best of our knowledge, this is the first case report of a PIK3CA inhibitor for the treatment of primary metastatic EMPD, and the treatment efficacy was good. PIK3CA inhibitors may be promising for the treatment of metastatic EMPD in the future.