Paget Disease of the Breast
Differential Diagnosis
| Pagetoid Squamous Cell Carcinoma In Situ |
Mammary Paget Disease |
| Atypical cells usually merge with surrounding keratinocytes |
Discrete population of atypical cells |
| Atypical cells may keratinize |
Atypical cells may form lumens or be mucin positive |
| Desmosomes and keratohyaline granules may be visible in atypical cells |
Desmosomes and keratohyaline granules not present |
| HMWCK+, p63+, CK7 negative |
CK7 >95%+, p63 negative, HMWCK rare |
| GCDFP15 negative |
GCDFP15 50%+ |
| Melanoma In Situ |
Mammary Paget Disease |
| Substantial proportion of atypical cells sit directly on the epidermal basement membrane |
Atypical cells at all levels but frequently have at least one layer of normal cells separating them from the basement membrane |
| No lumen formation or mucin positivity |
Atypical cells may form lumens or be mucin positive |
| CK7 and other keratins negative |
CK7 and other broad spectrum antikeratins >95%+ |
| S100 nearly 100%+ |
S100 0-26%+ |
| HMB45 and MelanA 60-95%+ |
HMB45 and MelanA negative |
Rare cases of Paget disease are pigmented
| Toker Cells |
Mammary Paget Disease |
| Small-medium sized bland cells |
Large atypical cells |
| No epidermal reaction |
Epidermis generally shows reactive changes |
Both are CK7+
Both may show small lumens (less frequently with Toker cells)
Both have pale cytoplasm
Toker cells are normal inhabitants of the nipple epidermis (see Lundquist 1999)
Merkel cells may also be CK7+
