A proposal for a TNM staging system for extramammary Paget disease: Retrospective analysis of 301 patients with invasive primary tumors.

Abstract Background Although extramammary Paget disease (EMPD) usually appears as carcinoma in situ, it sometimes becomes invasive (iEMPD) and fatal. However, a TNM staging system for iEMPD has yet to be established. Objective The aim of this study was to establish a TNM staging system for iEMPD. Methods We retrospectively collected iEMPD patients treated at 12 institutes in Japan. Factors reported to be associated with survival such as distant metastasis, lymph node (LN) metastasis, and primary tumor status were evaluated using the log-rank test. Results We enrolled 301 iEMPD patients, of whom 114 had remote metastases (49 had both distant and LN metastasis; 2, distant metastasis only; and 63, LN metastasis only) and the remaining 187 patients had no remote metastasis. Distant metastasis (M1) showed worse survival ( P P P  = 0.02). Lastly, in the analysis of the 187 patients without metastasis, tumor thickness of over 4 mm or lymphovascular invasion showed worse survival (T2, P P Conclusion We propose a TNM staging system for EMPD using simple factors for classification that could provide important prognostic information in managing EMPD. However, accumulation of more patient data and further revision of the system are required.