Invasive Paget disease of the breast: 20 years of experience at a single institution.

Mammary Paget disease with dermal invasion (invMPD) is rare, and its prognosis remains largely unknown. We reviewed MPD cases diagnosed at our institution and analyzed the clinicopathological characteristics of invMPD and non-invMPD to compare their incidences and outcomes. We retrospectively reviewed 205 cases of women diagnosed as having MPD between 1994 and 2013. Sixteen of 205 MPD cases (7.8%) had dermal invasion. Twelve of 16 invMPD cases had separate, underlying invasive breast carcinoma, and 3 invMPD cases had ductal carcinoma in situ. To exclude the influence of underlying disease on prognosis, we compared prognosis of invMPD with matched non-invMPD. The mean depth and extent of Paget cell invasion in invMPD cases were 0.637 and 1.268 mm, respectively. The horizontal extent of MPD was significantly larger in invMPD versus non-invMPD (mean, 14.31 mm versus 7.35 mm; P = .002). Distant metastasis and disease-related death were observed in 12.6% (24/189) and 12.1% (23/189) of non-invMPD patients, respectively, compared with 6.3% (1/16) and 6.3% (1/16) of invMPD patients; this difference was not significant (P = .7 and P = .7). Clinical outcomes of the invMPD patients were also not significantly different from the matched non-invMPD patients. In this study, MPD extent significantly correlated with MPD invasion. However, other clinicopathological parameters were not associated with dermal MPD invasion. Dermal MPD invasion was rare and did not predict regional lymph node metastasis or poor prognosis. The prognosis is usually similar for invMPD and non-invMPD, and MPD must be distinguished from locally advanced breast cancer presenting as satellite skin nodules.