Mixed epithelial and stromal tumours of the kidney with malignant transformation: a clinicopathological study of four cases

Mixed epithelial and stromal tumour of the kidney is a complex benign neoplasm in which malignancy rarely arises. In this study, we report four mixed epithelial and stromal tumours in which sarcoma or carcinoma developed. In the first, a multifocal adenocarcinoma arose and areas of transition from benign to malignant epithelium were observed. Oestrogen and progesterone receptors were diffusely present in the nuclei of the spindle cell stroma of the benign component. The second was a sarcoma in which benign epithelial elements were intermixed. Outside the renal parenchyma, clusters of small benign glands surrounded by oestrogen receptor-positive benign stroma were present, supporting the diagnosis of mixed epithelial and stromal tumour. Fluorescence in situ hybridisation for SYT-SSX translocation and immunohistochemical results, specifically TLE1 -ativity, argued against primary renal synovial sarcoma. The patient died 24 months after surgery. The third tumour consisted of small blue round cells, positive for epithelial membrane antigen, BCL2, CD99, and FLI1. Throughout the tumour, the presence of benign appearing branching tubules in fibromuscular stroma, reactive for smooth muscle actin, desmin and progesterone receptor, supported the diagnosis of mixed epithelial and stromal tumour in which a small round blue cell sarcoma with EWSR1 rearrangement arose. In the fourth tumour, adenocarcinoma with papillary architecture arose in a typical mixed epithelial and stromal tumour. In summary, we present four cases of mixed epithelial and stromal tumour with malignant transformation, two showing carcinomatous and the other two with sarcomatous transformation. Identification of typical benign looking elements and the absence of SYT-SSX translocation are helpful in recognition of this entity.

Malignant mixed epithelial and stromal tumour of the kidney: a case report and a literature review

Introduction.

Mixed epithelial and stromal tumour of the kidney (MEST) is a rare and distinctive neoplasm accounting for 0.2% of all renal cancers. Most of these tumours behave in a benign fashion but 13 cases with malignant transformation have already been reported. We present the first case of an extremely aggressive MEST with rapid recurrence after radical treatment, demonstrating objective response to chemotherapy.

Case presentation.

A 31-year-old female presented to the hospital complaining of gross hematuria. Computed tomography (CT) revealed an intraparenchymal mass in the left kidney forming a tumour thrombus in the inferior vena cava (IVC). Metastatic disease was ruled out and, under the clinical diagnosis of renal cell carcinoma, left radical nephrectomy with IVC thrombectomy was performed. The histopathological examination confirmed malignant MEST of the kidney. At the follow-up 12 months after surgery, a recurrent tumour in the left paravertebral area and a tumour thrombus in the IVC were detected. A second surgery was recommended and the mass from the paravertebral area was removed, so resection of the IVC with prosthetic replacement was performed. The histopathologic examination confirmed a recurrent malignant MEST. At the follow-up three months after the second surgery disease progression was diagnosed, so chemotherapy with ifosfamide and doxorubicin was initiated. The CT scan performed 14 months after the chemotherapy confirmed a stable process of the disease with no signs of progression.

Conclusions.

A literature review and our case report confirm the existence of extremely aggressive malignant MEST that shows response to chemotherapy. However, more reports are needed to improve our understanding about the biology of the MEST to develop any recommendations on personalized therapy.