Renal myxoid tumour of uncertain malignant potential

Report of two primary renal tumors with myxoid features. Differential diagnosis between benign and malignant entities

Renal mesenchymal neoplasms are rare entities which can have a benign or a malignant behavior. Herein we describe two renal mesenchymal tumors with myxoid stroma, investigating the wide spectrum of differential diagnosis. With our first case we considered some benign entities such as myxoma, myxoid leiomyoma, and mixed epithelial and stromal tumor; with our second case we considered some sarcomas with myxoid features such as myxofibrosarcoma, low-grade fibromyxoid sarcoma, dedifferentiated liposarcoma, and myxoid liposarcoma. During the diagnostic process, it is important to integrate histopathological, immunohistochemical, and molecular data in order to avoid misdiagnosis. We concluded our second case report was a myxofibrosarcoma grade 1. To the best of our knowledge, we described the fourth primary renal myxofibrosarcoma reported in literature.

Primary renal myxofibrosarcoma

Kidney sarcomas are rare, representing only 1% of malignant renal tumors. We herein report the case of a 70-year-old woman that was admitted for an episode of confusion in relation to hypertensive encephalopathy. Imaging investigations revealed a large mass in the right kidney with extension to the renal hilum. The patient underwent right open radical nephrectomy. The histopathologic study disclosed a 15-cm, myxoid and cellular, pleomorphic tumor with elongated, curvilinear, thin-walled vessels, and focal necrosis that involved the upper and middle segments of the kidney. Immunohistochemically, the tumor cells showed strong positivity for vimentin, bcl2 protein (nuclear staining pattern), CD34, CD99, and alpha-methylacyl coenzyme A racemase. The tumor was diagnosed as myxofibrosarcoma (MFS) grade 2 according to the FNCLCC system. To the best of our knowledge, this is the first report of an MFS arising from the kidney. Thus, MFS is an uncommon soft tissue tumor that can exceptionally arise from the kidney. The differential diagnosis with other myxoid tumors is of vital importance because it includes lesions with subtle differences and extremely variable biological behavior. Radical surgery is the treatment of choice. Long-term follow-up is recommended because of the tumor's capability for local recurrence and distant metastasis.