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| Differential diagnosis of common breast spindle cell lesions |
| Benign | Histological Features | Immunohistochemistry |
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| Fibromatosis | Collagen deposition amongst spindle cells arranged in fascicles infiltrating fatty tissue. Lymphoid aggregates may be seen at the margins of the lesion. | Positive: SMA, B-catenin (80% nuclear),
Negative: S100M CKs, p63, desmin,CD34 |
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| Myofibroblastoma | Irregular, nonencapsulated spindle cells with collagen bundles. Rare/No mitoses. No epithelial component seen. | Positive: desmin, SMA, CD34, ER, AR caldesmon, vimentin, Bcl2 and CD99.
Negative: S100, CKs, p63, RB STAT6 |
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| Neurofibroma | Bundles of wavy spindle cells, elongated nuclei and narrow cytoplasmic processes. | Positive: Neurofilament, S100 |
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| Schwannoma | Similar to Neurofibroma but characteristic Verocay Bodies with nuclear palisading, Antoni A & B areas | Positive: Neurofilament, S100 |
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| Nodular Fasciitis | Fibroblasts with vesicular nuclei in myxoid stroma. Mitoses frequently detected. Rapidly growing lesion arising from superficial fascia | Positive: SMA, vimentin,
Negative: S100,CD34,desmin, keratin |
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| Malignant | | |
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| MPNST | Types: Glandular, Epitheliod, mesenchymal. Spindle cells in dense cellular areas of high mitotic activity. Areas of necrosis, nuclear pleomorphism | Positive: Neurofilament, S100 p53
Negative: EMA, keratin |
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| Metaplastic Carcinoma | Malignant epithelial and mesenchymal areas. High mitotic figures, necrosis and nuclear pleomorphism. DCIS may be seen. | Positive: CKs, p63, vimentin, keratin
Negative: CD34 |
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| Malignant Phyllodes | Leaf-like morphology, marked stromal cellularity and nuclear pleomorphism. | Positive/Negative: CD34
Negative: CKs |
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| Melanoma | Can be composed of epitheliod +/spindle cells. Can have large pleomorphic cells. | Positive: S100, Melan A,
Negative: CKs |
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| Angiosarcoma | Haemorrhagic mass composed of epitheliod or spindle cells displaying vascular differentiation | Positive: CD31,CD34, keratin |
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