- Gross: these tumors tend to be more firm and gray with pushing borders.
- Histology: spindle cell proliferation, usually with focal areas that have typical appearance of clear cell RCC.
- Differential diagnosis: leiomyosarcoma -- the distinction can be made by a) finding areas of more typical RCC (requires extensive sampling) or b) by doing immunohistochemical stains for epithelial membrane antigen (EMA). EMA -- as the name suggests -- is produced by epithelial cells (which form carcinomas) and is generally not produced by mesenchymal cells (which form sarcomas). Thus, if you’re trying to get to the right diagnosis, a positive EMA stain in a spindle-cell neoplasm of the kidney suggests that the lesion is actually a carcinoma (in this case, RCC) whereas a negative EMA stain -- preferably paired with a positive stain for smooth muscle markers -- would support a diagnosis of sarcoma (in this case, leiomyosarcoma).
Remember:
Sarcomatoid RCC is much more common than leiomyosarcoma of the kidney, so always look carefully for typical RCC areas before committing to a diagnosis of leiomyosarcoma.
|
)
)
)
)