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| *Melanoma = classically pigmented, often a prominent [[red nucleolus]], a mix of spindle cells and epithelioid cells, mix of cohesive and dyscohesive cells. | | *Melanoma = classically pigmented, often a prominent [[red nucleolus]], a mix of spindle cells and epithelioid cells, mix of cohesive and dyscohesive cells. |
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| ===Histomorphologic classification=== | | ===A practical histomorphologic differential diagnosis of malignancy=== |
| Types of cells:
| | <center> |
| *[[Spindle cell]]:
| | {{familytree/start}} |
| **Tapered at both ends.<ref>URL: [http://www.medterms.com/script/main/art.asp?articlekey=25657 http://www.medterms.com/script/main/art.asp?articlekey=25657]. Accessed on: 18 January 2010.</ref>
| | {{familytree | | | | | | | | | | | A | | | | | | | | | | |A=Malignancy}} |
| **Suggests mesenchyme, i.e. sarcoma, compatible with melanoma and some carcinomas.
| | {{familytree | |,|-|-|-|v|-|-|-|v|-|^|-|v|-|-|-|v|-|-|-|.| |}} |
| *Plasmacytoid cell.
| | {{familytree | B | | C | | D | | E | | F | |G |B=Large epithelioid tumours|C=Spindle cell tumours|D=Small blue cell tumours|E=Pleomorphic tumours|F=Clear cell tumours|G=Myxoid tumours}} |
| **Resemble a plasma cell: eccentric nucleus, moderate basophilic cytoplasm, +/-"clockface" chromatin pattern (clumping of chromatin at the periphery of the nucleus), +/-perinuclear hof (crescentic cytoplasmic clearing adjacent to the nucleus; represents abundant Golgi apparatus).
| | {{familytree/end}} |
| *Epithelioid cell.
| | </center> |
| **Looks like epithelium - cell borders touch neighbouring cells so that the cells collectively form a barrier.
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| *[[Small round blue cell tumour]]/lymphoid:
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| **Small cells with scant cytoplasm.
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| ***"Small" is classically 2x a "resting lymphocyte" diameter.
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| ****Diameter of a "resting lymphocyte" ~ diameter of a [[red blood cell]] (RBC) ~ 8 micrometres.
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| ****Most carcinoma cells are 3-4x the size of a RBC.
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| *Small lymphoid ([[small cell lymphoma]]).
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| **"Small" in the context of lymphoid is classically ~1x a "resting lymphocyte" diameter.
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| **Often not malignant by cytology.
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| ==Differential diagnosis by site== | | ==Differential diagnosis by site== |