Three case reports and a literature review of HER-2-overexpressing mammary Paget’s disease combined with invasive breast cancer

To investigate the clinicopathological characteristics, treatment, and short-term outcomes of human epidermal growth factor receptor 2 (HER-2)-overexpressing mammary Paget’s disease (MPD) combined with invasive ductal carcinoma (IDC), with an emphasis on the high proportion of HER-2-overexpressing subtype, the discordance between tumor size and lymph node burden, and the feasibility of immediate breast reconstruction. A retrospective analysis was conducted on the clinical data of three patients with HER-2-overexpressing MPD-IDC treated at our hospital, supplemented by a narrative literature review. Detailed case presentations, treatment timelines, and a summary table were provided in accordance with CARE guidelines. All three patients were female, aged 41–64 years, and presented with nipple erosion, discharge, or a breast mass. Postoperative pathology confirmed MPD-IDC in all cases, with immunohistochemistry showing HER-2 (3+), and both estrogen receptor (ER) and progesterone receptor (PR) negative. All patients received comprehensive therapy including surgery, postoperative chemotherapy, and anti-HER-2 targeted therapy. During the 4–28 months of post-operative follow-up, no recurrence or metastasis was observed. Notably, in Case 3, the primary tumor was extremely small (0.5 cm) but extensive axillary lymph node involvement (14/27) was present, suggesting aggressive clinicopathological behavior in this HER-2-overexpressing MPD-IDC case. This finding highlights a clinically relevant discordance between the measured invasive tumor size and nodal burden, but it should be interpreted as a descriptive and hypothesis-generating observation. All three patients received standardized anti-HER-2 targeted therapy and achieved favorable short-term outcomes. The HER-2-overexpressing subtype is a common molecular subtype in MPD-IDC, with typical clinical manifestations that are easily overlooked. Standardized comprehensive treatment, particularly systemic therapy including anti-HER-2 targeted therapy, appears important for improving patient prognosis. Unique features such as the marked tumor size-node burden discordance observed in one patient suggests that invasive tumor size alone may not fully reflect regional metastatic risk in selected cases, especially when suspicious axillary nodes are present. These observations remain descriptive and require validation in larger series with longer follow-up.