LETTER TO EDITOR
Year : 2008 | Volume
: 51 | Issue : 4 | Page : 573--576
Primary pleomorphic undifferentiated sarcoma of the kidney: A rare renal tumor
Ruchika Gupta, Sampada Gupta, Deepti Aggarwal, Sompal Singh
Departments of Pathology, Maulana Azad Medical College and Hindu Rao Hospital, New Delhi, India
162, Pocket-B, Sarita Vihar, New Delhi - 110 076
|How to cite this article:|
Gupta R, Gupta S, Aggarwal D, Singh S. Primary pleomorphic undifferentiated sarcoma of the kidney: A rare renal tumor.Indian J Pathol Microbiol 2008;51:573-576
|How to cite this URL:|
Gupta R, Gupta S, Aggarwal D, Singh S. Primary pleomorphic undifferentiated sarcoma of the kidney: A rare renal tumor. Indian J Pathol Microbiol [serial online] 2008 [cited 2022 Oct 4 ];51:573-576
Available from: https://www.ijpmonline.org/text.asp?2008/51/4/573/43774
Malignant fibrous histiocytoma (MFH) is a common soft tissue sarcoma; however, its origin from the renal parenchyma or renal capsule is extremely rare having been reported in only a few cases.  We report a similar rare case of a 72-year-old male who presented with complaints of pain in the right upper abdomen for the past 1 year. This was associated with reduced appetite and loss of weight. However, there was no history of hematuria, voiding difficulty, or fever. A physical examination revealed a fixed, non tender mass in the right lumbar region. Routine investigations showed anemia (hemoglobin 8.4g/dl, hematocrit 25%) and a raised erythrocyte sedimentation rate (102 mm in the first hour). Biochemical studies were within normal limits. Imaging studies, including an abdominal ultrasonography (USG) and a computed tomography (CT) scan, revealed an 11x8 cm mass with inhomogeneous enhancement in the upper pole of the right kidney. There was extensive cortical destruction and the mass was extending into the renal vein. However, no involvement of the inferior vena cava or lymphadenopathy was noted. With a pre-operative diagnosis of renal cell carcinoma involving the right kidney, a right radical nephrectomy was performed.
Grossly, the specimen revealed a large, yellowish-white tumor measuring 10x8 cm with areas of hemorrhage and necrosis in the upper pole of the right kidney. There was renal vascular invasion; however, no perinephric fat infiltration was noted. Multiple sections showed a tumor composed of predominantly spindle cells arranged in short fascicles with interspersed histiocytic cells including multinucleated giant cells. Marked nuclear pleomorphism and brisk mitotic activity (10-12 per HPF) were seen. Areas of necrosis and focal inflammatory infiltrate were also present. The tumor was infiltrating into the adjacent renal parenchyma and extending to involve perinephric fat [Figure 1]. On immunohistochemistry, the spindle cells stained for vimentin, while histiocytic cells were positive for CD68. The tumor cells were negative for cytokeratin [Figure 2], epithelial membrane antigen, smooth muscle actin, and S-100 protein. Further immunohistochemistry could not be performed.
A final pathological diagnosis of primary malignant fibrous histiocytoma (pleomorphic undifferentiated sarcoma) of the right kidney was made.  The patient was referred for post-operative chemotherapy; however, he developed severe neutropenia with sepsis and died after receiving two cycles of chemotherapy.
Primary renal sarcomas, in general, are rare tumors and account for up to 3% of all renal malignancies.  No definite criteria have been defined for the diagnosis of primary renal MFH; however, it has been suggested that (1) there should be no history of sarcoma elsewhere to exclude metastasis, (2) the gross appearance must be compatible with origin in the kidney, (3) sarcomatoid renal cell carcinoma must be excluded, and (4) metastasis, if present, should be smaller than the renal tumor. MFH arising from renal parenchyma or capsule is an extremely rare phenomenon and constitutes less than 6% of renal sarcomas.  Only a few cases of renal MFH were found in the available literature.  We add another case of this rare entity to the literature.
In the current World Health Organization classification of soft tissue tumors, MFH is considered synonymous with pleomorphic undifferentiated sarcoma. In a recent consensus meeting, it was suggested that this terminology of MFH would be dropped in future classification. After exclusion of other differentiation, the tumor may be classified as an undifferentiated pleomorphic sarcoma.  The clinical features of the available previously reported cases of renal MFH are summarized in [Table 1]. A pre-operative radiologic diagnosis of MFH has not been possible in previous reports and simple or radical nephrectomy was undertaken with a suspicion of renal cell carcinoma.  Thus, histopathological examination remains the only modality for a correct diagnosis of this rare entity.
The histological differential diagnoses of renal MFH would include other benign and malignant lesions of the kidney. Xanthogranulomatous pyelonephritis (XGPN), a reactive renal pseudotumor, also shows histiocytes, mixed inflammatory infiltrates, and fibroblastic proliferation, which sometimes may show mitotic activity.  Reactive fibrohistiocytic proliferations associated with previous surgery or in response to foreign material may also cause a diagnostic dilemma.  The most important diagnostic problem is excluding sarcomatoid renal cell carcinoma. This may be achieved by extensive tissue sampling and immunohistochemistry (sarcomatoid carcinoma is positive for cytokeratin and vimentin while MFH is positive for vimentin but negative for cytokeratin).  A recently described entity, anaplastic sarcoma of the kidney (ASK), also needs to be considered. ASK was reported as a polyphenotypic tumor composed of a spindle cell component, round to oval cells in myxoid stroma, and divergent differentiation like chondroid and osteoid matrix. Widespread anaplastic nuclear features were noted in the reported cases. Immunohistochemistry performed on a few of the cases showed positivity for vimentin and desmin and negative staining for cytokeratin, MYOD1, NB84a, CD34, CD99, WT1, and CD56.  The reported cases underwent radical surgical excision as the therapeutic modality of choice. An incomplete resection leads to recurrence and poor prognosis. The prognosis of renal MFH is extremely poor- 25% of the reported patients died within 1 year of surgery. 
In conclusion, primary renal pleomorphic undifferentiated sarcoma (malignant fibrous histiocytoma) is an extremely rare tumor with no distinctive radiological features. The pathologists should be aware of the rare occurrence of this tumor in the kidney.
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