LAUSR

To the Editor: Loss of the SWI/SNF complex has recently been reported in carcinomas of various organs, including stomach, kidneys, upper urinary tract, and the lung. These carcinomas exhibited similar morphology, undifferentiated pleomorphic or rhabdoid morphology. For the first time, we report an undifferentiated pleomorphic renal carcinoma that developed in a patient with acquired cystic kidney, showing loss of the SWI/SNF complex. A 70-year-old male patient was admitted to our hospital presenting with a fever of unknown origin that had continued for 4 months. He had undergone hemodialysis for 22 years because of chronic glomerulonephritis. Positron emission tomography and computed tomography revealed a left renal tumor and with metastasis to the liver, bone, and paraaortic lymph node. We performed a left nephrectomy for volume reduction and to relieve the fever. After the operation, the patient had no complications and molecular-targeted drugs were administered. He survived with disease for 2 months. Macroscopically, the resected kidney had a multilocular cystic appearance, and a 4.5 4.0 3.5 cm tumor mainly located in the lower pole. The cut surface of the tumor was a whitish solid mass with necrosis and hemorrhage. We prepared 40 hematoxylin-eosin stained slides by whole sectioning of the resected kidney. Microscopically, the carcinoma had invaded the perirenal and sinus fat. Lymphovascular invasion was prominent and the carcinoma was involved in the renal vein. The carcinoma exhibited solid growth (Fig. 1a) with foci of cribriform-like architecture composed of intraand inter-cytoplasmic lumina. The carcinoma had massive necrosis accompanied by prominent inflammatory cells. Carcinoma cells were large and pleomorphic with rhabdoid foci of (Fig. 1b) and spindle cell formation (Fig. 1c). The spindle cells were not prominent and were intermingled with pleomorphic cells. Scattered carcinoma cells with bizarre nuclei and multinucleation were observed. A few oxalate crystals were seen in the carcinoma (Fig. 1b). The carcinoma was composed of only undifferentiated pleomorphic area, without area of differentiated renal carcinoma. Immunohistochemically, the carcinoma was positive for PAX8 and CD10. AMACR was positive for 10% of carcinoma cells and S100A1 was positive for 30% of carcinoma cells. A few carcinoma cells were positive for SALL4. GATA3, carbonic anhydrase IX, RCC marker, CK7, c-kit, ksp-cadherin, CK34bE12, TFE3, OCT3/4, glypican 3, ALK(5A4), and mismatch repair protein (MLH1, MSH2, MSH6, and PMS2) were negative. P53 expression was completely lost. We could not clarify whether the carcinoma had dedifferentiated from another differentiated renal neoplasm or the carcinoma had developed de novo. We supposed that the carcinoma could be classified as acquired cystic disease-associated renal cell carcinoma (ACD-RCC) because the patient had a long history of hemodialysis, and oxalate crystal deposition and cribriform-like growth were observed, but this was contradicted by the tumor's immunoprofile, which was atypical for ACD-RCC: immunonegative for AMACR and RCC marker. Accordingly, we diagnosed the carcinoma as undifferentiated pleomorphic renal carcinoma, pT3aN1M1, Stage 4 (UICC 8th). Additionally, we performed immunohistochemical analysis for seven members of the SWI/SNF complex: SMARCA2, SMARCA4 (BRG1), SMARCB1 (INI-1), SMARCC1, SMARCC2, ARID1A, PBRM1 (BAF180). We demonstrated loss of SMCARCA2 (Fig. 1d), SMARCB1 (Fig. 1e), and PBRM1 (Fig. 1f); the other antibodies against the SWI/SNF complex showed intact. The loss of INI-1 expression has only been reported in renal medullary carcinoma and some collecting duct carcinomas in adult renal tumors. Recently, it was reported that putative dedifferentiated renal carcinoma from clear cell renal carcinoma, papillary renal cell carcinoma, and chromophobe renal cell carcinoma showed loss of some constituents of the SWI/SNF complex. However, loss of the SWI/SNF complex had not previously been reported in ACD-RCC or renal cell carcinoma in acquired cystic kidney. We could not demonstrate dedifferentiation from ACD-RCC in this case. However, we suggest that loss of SWI/SNF might be associated with the undifferentiated pleomorphic morphology, including rhabdoid and spindle cells, irrespective of the background of tumor development. To our knowledge, co-loss of SMARCA2, SMARCB1, and PBRM1 has not been reported in renal carcinoma. Further study will be required to determine whether this loss pattern is characteristic of renal cell carcinoma developed in ACD. In conclusion, we reported the loss of the SWI/SNF complex in an undifferentiated renal carcinoma developed in acquired cystic kidney and show a previously unreported co-loss pattern of the SWI/SNF complex in renal