Histiocytic Sarcoma in the Kidney: A Rare Presentation

Abstract

Abstract Background Histiocytic sarcoma is a rare neoplasm of mature histiocytes with a wide range of clinical presentations and manifestations. The heterogeneity of this neoplasm can cause difficulty in both diagnosis and treatment. It is a diagnosis of exclusion, requiring verification of the histiocytic lineage and the exclusion of other B-cell related malignancies. Although cases of postrenal transplant histiocytic sarcoma have been reported, incidences in a native kidney are rare. Case Report We present the case of a 70-year-old male with a history of colorectal adenocarcinoma, status post chemotherapy, with an incidental exophytic renal mass found on imaging, which was determined to be a sarcomatoid renal cell cancer on biopsy. Radical nephrectomy was performed, revealing a 4.5 × 3.5 × 3.2-cm mass invading the renal pelvis and fat. Microscopic examination of the tumor showed large, poorly cohesive neoplastic cells with abundant pale, eosinophilic cytoplasm that stained positive for vimentin, CD4, CD163, and CD68 and weakly/focally positive for lysozyme. Negative immunostains included PAX-8, pan-CK, AE1/AE3, HMB45, S100, CD34, CD30, ALK1, CD1a, myeloperoxidase, CD138, myo-D1, SMA, and CD21. A diagnosis of histiocytic sarcoma, grade 4 was made based on these findings. Discussion Histiocytic sarcoma is a disease of unknown etiology accounting for less than 1% of all hematolymphoid neoplasms. Our literature review revealed no other cases arising de novo in the kidney, but several cases were reported in postrenal transplant patients. Diagnosis of histiocytic sarcoma is difficult as it is a diagnosis of exclusion. The immunohistochemical profile most often expresses lysosome-related markers, such as CD68, CD163, or lysozyme. Additionally, negative staining is expected for markers related to B cells, T cells, and melanocytes. The cells are often large with eosinophilic cytoplasm, well-defined borders, and vesicular chromatin. Although there are numerous differentials, distinct morphologic and immunohistochemical features allow for accurate diagnosis.