Postoperative radiation therapy improves prognoses in extramammary Paget's disease presenting with multiple lymph node metastases

Invasive extramammary Paget's disease may cause lymph node and distant metastases. Complete lymph node dissection is generally performed for extramammary Paget's disease presenting with lymph node metastases. Patients with extramammary Paget's disease and multiple lymph node metastases typically have poor prognoses, and there is no effective postoperative treatment to prevent recurrence or further metastases in such patients to date. This study aimed to evaluate the efficacy of postoperative radiotherapy in patients with extramammary Paget's disease and multiple lymph node metastases. We enrolled 26 patients with extramammary Paget's disease with ≥3 lymph node metastases who were treated at the National Cancer Center Hospital in Japan between January 2000 and June 2021. The patients were divided into those who underwent complete lymph node dissection only or with postoperative radiotherapy. We evaluated recurrence‐free survival, distant metastasis‐free survival, and overall survival outcomes with Kaplan–Meier curves. Among the 26 enrolled patients, 16 underwent complete lymph node dissection only and 10 underwent complete lymph node dissection with postoperative radiotherapy. The median follow‐up period was 16 months. The 5‐year recurrence‐free, distant metastasis‐free, and overall survival values were 47.3%, 63.0%, and 90% in those with complete lymph node dissection and postoperative radiotherapy, while these outcomes were all 0% (p = 0.001, 0.004, and 0.009, respectively) in those with only complete lymph node dissection. Thus, survival was significantly prolonged with postoperative radiotherapy. Additional postoperative radiotherapy may substantially improve the prognoses of patients with extramammary Paget's disease and ≥3 lymph node metastases, and undergoing curative surgery.