Special Immunohistochemical Stains

Photomicrographs contributed by Dr. Sanjay Kakkar.

Figure 1. Keratin

The tumor cells did not stain for keratin, a marker found in most epithelial tumors. Note the strong positive staining of the overlying epithelium.

Figure 2. Chromogranin

A stain for chromogranin to indicate neuroendocrine differentiation was negative, helping to exclude carcinoid and atypical carcinoid tumors, as well as small cell carcinoma.

endothelium

Figure 3. Smooth Muscle Specific Actin

This stain is strongly positive in the cytoplasm of most cells. Note that the epithelium and endothelial cells are negative.

Find a vessel with non-staining endothelium.

Figure 4. Vimentin

A stain for vimentin, which is present in cytoplasmic filaments, was also strongly positive in the tumor cells. The presence of vimentin is not specific for this tumor: most cells of the body stain for it. Note that the endothelial cells and stromal cells are also positive.

Further, a stain for collagen IV of basement membrane was positive around each tumor cell.

A stains for S100 (neural marker) was negative.

What is the diagnosis?

Answer

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Vessel with non-staining endothelium

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The diagnosis is malignant glomus tumor.

Predominantly rounded cells with central nuclei, a vascular component, and positive stains for smooth muscle actin, vimentin, and pericellular collagen IV (negative stains for keratin and chromogranin) are features of glomus tumor. While a diagnosis of epithelioid leiomyoma/leiomyoblastoma was also considered, staining for collagen IV around each cell does not occur in such tumors. The collagen IV represents the basement membrane seen ultrastructurally in glomus tumors. The high cellularity and mitotic rate, and location in the lung are features suggestive of malignancy.

Compare this tumor to a benign glomus tumor (use the "back" button in the menu to return).

This low-power view shows a pattern of uniform, rounded cells and prominent vasculature similar, except for hypercellularity, to its benign counterpart. This pattern helps to confirm the diagnosis of glomus tumor.

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