Clinicopathological Characteristics and Survival Outcomes in Mammary Paget's Disease: a Retrospective Study Based on a Chinese Population

Background: Mammary Paget's disease (PD) is a rare type of breast cancer. Most cases of PD is presented with underlying ductal carcinoma in situ (DCIS) or invasive breast carcinoma (IDC). This study aimed to investigate the clinicopathological characteristics and survival outcomes of PD patients. Materials and Methods: A total of 406 patients diagnosed with PD with IDC/DCIS at Fudan University Shanghai Cancer Center (FUSCC) were recruited as the PD group, 1218 patients diagnosed with IDC/DCIS alone during the same period were selected as the non-PD group, and the clinicopathological results of these two groups were compared. The Surveillance, Epidemiology, and End Results (SEER) database was used to investigate the clinicopathological features between PD and non-PD patients for validation. Then, a matched group study was performed to compare the survival of PD and non-PD patients.Results: Compared with the non-PD group, the PD group was much more likely to have larger (≥2 cm: 43.1% vs. 35.5%, P<0.001), less hormone receptor (HR)-positive (68.5% vs. 26.6%, P<0.001), more human epidermal growth factor receptor-2 (HER-2)-positive (70.7% vs. 27.5%, P<0.001) and higher Ki-67 proportion (51.5% vs. 42.5%, P<0.001) tumors. The HER-2 overexpression subtype accounted for the largest proportion in the PD-IDC group and the lowest proportion in the non-PD-IDC group (54% vs. 8%, P<0.01). Moreover, the PD group had significantly worse disease-free survival (DFS) than the non-PD group (5-year DFS: 91.8% vs. 97.3%, P=0.001), and the SEER database showed a similar trend. Univariate and multivariate Cox regression analyses demonstrated that PD was an independent poor-risk factor for breast cancer survival. Our matched study showed that the PD group had worse survival than the non-PD group after excluding age, HR, HER-2, tumor size and lymph node status.Conclusions: PD with IDC/DCIS is associated with more aggressive tumor characteristics and worse survival outcomes. More than half of PD breast cancers are of the HER-2 overexpression subtype. PD is an independent poor-risk factor for breast cancer survival.