Clear cell sarcoma of kidney in an adolescent and in young adults: a report of four cases with ultrastructural, immunohistochemical, and DNA flow cytometric analysis.

Clear cell sarcoma of the kidney is a distinct, highly malignant pediatric neoplasm. Its occurrence in adults is extremely rare and the subject of isolated case reports. We present a series of four cases (three males and one female) identified in an adolescent and in young adults (16, 18, 20, and 25 years) with flank mass (three cases), hematuria (two cases), flank pain (two cases), and hypertension (one case). Three patients had stage III disease and one had stage I disease (National Wilms' Tumor Study staging system). All tumors had predominantly or exclusively the classic histology of a monotonous proliferation of uniform small round cells with evenly distributed fine chromatin, although focal microcyst formation (two cases) and spindled architecture (one case) (variant patterns) were also noted. Therapy in all cases consisted of surgery and chemotherapy with or without radiation. Follow-up data (29-202 months) showed distant metastases in all four cases, including the lung (four cases), bone (two cases), and the liver (two cases). Three patients died of disease at 29, 59, and 63 months (mean, 50.3 months), and one patient is alive with no evidence of disease at 202 months. Ultrastructural features included scattered primitive junctions, short and irregular cytoplasmic extensions, and scant to a moderate amount of mitochondria. Immunohistochemical study (three cases) showed immunoreactivity with vimentin (two cases) and no reaction with cytokeratin, epithelial membrane antigen, S-100 protein, or desmin. Flow cytometric analysis showed diploid DNA content in three primary tumors and tetraploidy in one metastatic tumor. The proliferative activity (S-phase fraction) was low to intermediate (mean, 9.8%). Our data suggest that clear cell sarcoma of the kidney in the young adult age group resembles its pediatric counterpart in ultrastructural and immunohistochemical characteristics, proclivity for skeletal and visceral metastasis, DNA diploid status with relatively low S-phase, and aggressive clinical course. Clear cell sarcoma of the kidney in adult patients, although rare, must be differentiated from sarcomatoid carcinoma, sarcomas, and round cell tumors because of its unique characteristics in comparison to other renal neoplasms.