In sarcomatoid renal cell carcinoma (RCC),
it is generally accepted that the sarcomatoid portion is
derived from metaplastic transformation of carcinoma.
Sarcomatoid RCCs account for about 1-8% of all renal
tumors. Macroscopically, tumors generally form
encapsulated masses and show invasive growth.
Sarcomatoid RCCs originate from all subtypes of RCCs,
including conventional, papillary, chromophobe, and
collecting duct carcinomas. With regard to the growth
pattern of the sarcomatoid component, malignant fibrous
histiocytomatous, fibrosarcomatous and unclassified
sarcomatous patterns are frequently seen.
Immunohistochemically, sarcomatoid RCCs are
generally positive for AE1/AE3, epithelial membrane
antigen (EMA) and vimentin and negative for desmin,
actin and S-100. Little is know about genetic alterations
in sarcomatoid RCCs. Further studies are therefore
needed to identify the key gene involved in sarcomatoid
transformation of RCCs