Treatment outcomes of advanced/metastatic extramammary Paget's disease in Korean patients: KCSG‐RC20‐06

Abstract Background Extramammary Paget's disease (EMPD) is rare. There are no standard treatments due to its rarity and few clinical trials. Methods The objective of this multicenter study was to investigate treatment outcomes of Korean patients with advanced/metastatic EMPD. Data were collected retrospectively from 14 institutions participating in Korean Cancer Study Group (KCSG) Rare Cancer Committee. Results A total of 37 patients were identified. Of these 37 patients, 6 received locoregional therapy as a first‐line treatment. In 31 patients who received systemic chemotherapy as a first‐line treatment, platinum‐based chemotherapy (n = 22) achieved an objective response rate (ORR) of 45.5% and a median progression‐free survival (PFS) of 7.89 months. Taxane‐based chemotherapy (n = 8) achieved an objective response rate of 62.5% and median PFS of 9.73 months. In second‐line chemotherapy, platinum‐based chemotherapy (n = 4) had a disease control rate (DCR) of 75.0% and median PFS of 3.45 months. Taxane‐based chemotherapy (n = 8) had a DCR of 75.0% and a median PFS of 8.67 months. Six patients received anti‐human epidermal growth factor receptor 2 (HER2) antibody during first‐ and second‐line chemotherapy. Overall, systemic chemotherapy combined with anti‐HER2 antibody had an ORR of 100% and a median PFS of 13.31 months. The ORR and PFS with systemic chemotherapy combined with trastuzumab was better than platinum‐ and taxane‐based chemotherapy only. Conclusions Due to its rarity, advanced or metastatic EMPD still has no established standard treatment. Results of our study indicate that the combination of trastuzumab with taxane has longer survival than trastuzumab monotherapy or conventional platinum‐ or taxane‐based chemotherapy.