Expression of cyclin D1 in clear cell sarcoma of kidney. Is it useful in differentiating it from its histological mimics?

Background: Clear cell sarcoma of the kidney (CCSK) is a rare malignant pediatric renal neoplasm with a heterogeneous histological appearance which often results in misdiagnosis. There are no specific immunohistochemical markers which can help in differentiating CCSK from other pediatric renal neoplasms. Recently Cyclin D1 has been investigated as a possible marker in this regard. In this study, we aim to determine the usefulness of Cyclin D1 in differentiating between CCSK and other pediatric renal neoplasms and to compare our results with those of recently published studies. Methods: A total of 48 cases of CCSK, Wilms tumor (WT), renal rhabdoid tumor, mesoblastic nephroma, renal Ewing sarcoma and neuroblastoma were included in the study. All cases were stained with cyclin D1. Extent of Cyclin D1 staining was graded according to percentage of positive tumor cells as diffuse (> 70%), focal (5 to 70%), and negative (< 5%). Intensity of Cyclin D1 staining was graded as strong or 3+, moderate or 2+ and weak or 1 +. Results: Most or all cases of CCSK, neuroblastoma and renal Ewing sarcoma demonstrated diffuse and strong positivity for Cyclin D1. Most cases of Wilms tumor (epithelial component) also demonstrated diffuse and often strong positivity for Cyclin D1. In most cases of WT, blastemal component was negative. Conclusions: Cyclin D1 is a sensitive but not specific immunohistochemical marker for CCSK and many other pediatric renal malignant neoplasms as well as for neuroblastoma. Hence, careful examination of histological features is important in reaching an accurate diagnosis in CCSKs. However, Cyclin D1 is very helpful in distinguishing between blastema-rich WT and CCSK.