Figure 5

Tumors excluded from the category of renal cell carcinoma with angioleiomyoma-like stroma: Two tumors had a prominent component of smooth muscle-like stroma containing numerous blood vessels in only one of the tumor sections (a), whereas the remainder of the tumor had a typical morphological appearance (b) and immunohistochemical profile of clear cell renal cell carcinoma. This was interpreted as tangential sectioning of the tumor pseudocapsule in one tissue block. Four clear cell renal cell carcinomas contained bundles of smooth muscle in multiple tumor sections (c). The smooth muscle demonstrated strong positive labeling for caldesmon (inset); however, otherwise the immunoprofile was typical of clear cell renal cell carcinoma and chromosome 3p deletion was often present. This situation was interpreted as the result of invasion of adjacent structures. One unclassified renal cell carcinoma (d) was thought morphologically to have smooth muscle stroma; however, immunohistochemical staining for smooth muscle actin (inset) and caldesmon (not pictured) highlighted only the intratumoral blood vessels and not the spindle-shaped cells. The spindle-shaped cells also labeled for some epithelial antigens, supporting exclusion from this category. Two unclassified renal cell carcinomas (e) were composed of nests of cells with clear cytoplasm in a prominent stroma. Although immunohistochemical features overlapped with renal cell carcinoma with angioleiomyoma-like stroma, extent of labeling for carbonic anhydrase IX was less and chromosome 3p deletion was present. One unclassified renal cell carcinoma (f) was composed entirely of complex papillary architecture. Immunohistochemical and molecular features were similar to those of renal cell carcinoma with angioleiomyoma-like stroma; however, due to the contrasting exclusively papillary morphology, this tumor could not be confidently placed in that category.