Selection: pulmonary lesions with a storiform or fascicular growth pattern. It is essential to exclude a metastatic focus, since the lungs are a common site of metastases from sarcomas.
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Histologic Feature
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Inflammatory Pseudotumor, Fibrohistiocytic Type
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Malignant Fibrous Histiocytoma, Storiform-Pleomorphic Type
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fibrohistiocytic proliferation
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bland with xanthoma cells
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atypical with increased nuclear hyperchromasia
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nuclear pleomorphism
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none to mild
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moderate to marked
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giant cells
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Touton
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bizarre
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mitotic rate in 50 high power fields (HPF)
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< 3 per 50 HPF
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>= 3 per 50 HPF
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atypical mitoses
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absent
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present
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tumor necrosis
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absent to rare
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present
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vascular invasion
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absent
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present
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metastases
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absent
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present
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where:
• Xanthoma cells are lipid-containing histiocytic cells.
• A microscopic high power field uses an objective lens of 40x ("high dry").
An inflammatory pseudotumor should have all of the listed features. It contains a mixture of lymphocytes, plasma cells and/or eosinophils together with the xanthoma cells and Touton giant cells.
According to Table 2 (page 1820) the diagnosis of malignant fibrous histiocytoma (MFH) requires >= 4 of the criteria.
Any tumor not meeting the criteria for inflammatory pseudotumor or MFH were classified as "borderline tumor". I personally would think that these could be called "probably malignant" if either:
(1) metastases are present
(2) 2 or more of the following are present (mitotic rate >= 3 per 50 HPF, tumor necrosis, vascular invasion, marked nuclear pleomorphism)
