Clinicopathological study of invasive extramammary Paget's disease: subgroup comparison according to invasion depth

Background Extramammary Paget's disease (EMPD) is a distinct form of malignant skin neoplasm. Invasive EMPD is relatively rare and its detailed histopathological features have not been investigated to date. Methods Surgical specimens were obtained from 51 patients with primary invasive EMPD. Clinical data including lymph node status were retrieved from the patients' medical records. Cases were divided into subgroups according to invasion depth: dermal invasion 1mm (minimal invasion) and dermal invasion >1mm in depth. Histological patterns (nodular/glandular pattern or micronodular pattern), lymphatic/venous invasion, mitosis and lymph node status were compared between the two groups. Results The invasive EMPDs included 26 cases (51.0%) with dermal invasion 1mm (minimal invasion) and 25 cases (49.0%) with dermal invasion >1mm in depth. Lymph node metastasis was detected in 2/26 (7.7%) patients with minimally invasive EMPD. Nodular/glandular pattern (72.0%), lymphatic/venous invasion (52.0%), mitosis (88.0%) and nodal metastasis (88.0%) were all significantly more frequent in cases with dermal invasion >1mm, compared to EMPDs with dermal invasion 1mm (minimal invasion) (P<0.001). Conclusion These results suggest that invasive EMPD can be divided according to invasion depth, with a cut-off depth of 1mm. This might represent the basis for a useful, EMPD-specific staging system.