Real‐World Efficacy of Chemotherapy in Patients With Advanced Unresectable Extramammary Paget Disease: A Retrospective Multicenter Study of 138 Japanese Patients

Extramammary Paget disease (EMPD) is a rare skin cancer with an estimated incidence rate of 0.13 per 100 000 population/year in Caucasians and 0.28 in Asians. Although distant metastases have been reported in 10%-20% of EMPD cases, standardized systemic chemotherapy has not been established. Prospective clinical trials are essential to establish standard treatments for advanced EMPD. Therefore, this retrospective study examined a substantial number of patients with EMPD to assess the efficacy of systemic chemotherapy. This study included 164 patients with advanced EMPD who underwent treatment at 16 Japanese institutions. Treatment efficacy was evaluated in a cohort of 138 patients, after excluding 26 patients without lesions outside the radical irradiation field from the 164 patients. The efficacy of each treatment was evaluated by determining the objective response rate (ORR), progression-free survival (PFS), and overall survival (OS) using Kaplan-Meier analysis. Multivariate analysis was performed to account for potential confounding factors, such as age, sex, and performance status. The patients received the following treatments: docetaxel hydrate (DOC) (65.9%); tegafur/gimeracil/oteracil potassium, DOC (S-1/DOC) (9.8%); fluorouracil and cisplatin (FP) (15.9%); and other drugs (8.5%). DOC is the most commonly used in Japan. The ORRs in the DOC, S-1/DOC, and FP groups were 51.6%, 78.6%, and 27.8%, respectively. Logistic regression analysis revealed that, compared with the DOC group, the odds ratio for the ORR of the S-1/DOC group was 3.29 (95% CI: 1.49-7.25, p = 0.003). However, no significant differences in OS or PFS were observed between the treatment groups (p = 0.122 and p = 0.422, respectively). This study provides valuable information on EMPD and may serve as a useful historical control for the future evaluation of new treatments for EMPD.