Usefulness of sentinel lymph node biopsy for prognostic prediction in extramammary Paget's disease

Background: Complete excision of the primary lesion has long been considered the standard treatment for extramammary Paget's disease (EMPD). However, the presence of lymph node metastases has been reported as an important prognostic factor. Objectives: We evaluated the association between lymph node metastasis and prognosis for EMPD using sentinel lymph node (SLN) biopsy. Materials and methods: This retrospective study included 59 patients with histopathologically-confirmed primary EMPD. A total of 45 patients with microinvasion to the papillary dermis and deep invasion into the reticular dermis or subcutaneous tissue were included in the analysis. The survival curves of the SLN-negative group and the SLN-positive group were compared and we examined the risk factors for SLN positivity. Results: A total of 139 SLNs were excised from one (28 patients) or both inguinal regions (31 patients). The average number of detected SLNs was 2.4. The incidence of SLN metastases was 16.9%. SLN positivity rates according to level of invasion were 0% for intraepithelial lesions, 4.1% for microinvasion, and 42.8% for dermal invasion. The five-year survival rates were 100% in the SLN-negative and 24% in the SLN-positive groups (p = 0.0001). Conclusion: Reticular dermis or subcutaneous tissue invasion was a significant independent risk factor for SLN positivity according to multivariate analysis. The result of SLN biopsy affected prognosis. It is extremely important to accurately ascertain the presence, i.e. the number, or absence of regional lymph node metastases in patients with EMPD. We conclude that SLN biopsy may be appropriate for cases where invasion is suspected.