Figure 6

Twenty-seven tumors with a range of morphologic features raising the possibility of SDH-deficient RCC were found to have positive immunohistochemical staining for SDHB and were excluded from the study group. Prominent cytoplasmic vacuoles were noted in 15 of these tumors. In one such example (a), abrupt transitions from areas of eosinophilic tumor cells to areas with numerous cytoplasmic vacuoles were present. Intense granular cytoplasmic labeling for SDHB was retained in this tumor (b), supporting exclusion from the category of SDH-deficient RCC. The cytoplasmic vacuoles were uniformly negative for SDHB, indicating that they are unlikely to be enlarged, abnormal mitochondria. Another unclassified RCC that was excluded from the SDH-deficient study group was unencapsulated and composed of cells with pale to flocculent cytoplasm with areas of cytoplasmic clearing (c). Numerous entrapped non-neoplastic renal tubules were present (center). Despite the pale-staining cytoplasm, positive staining for SDHB was readily recognizable by immunohistochemistry in both the neoplasm and entrapped tubules (d).