Case Diagnosis and Discussion
Diagnosis
Renal medullary carcinoma.
Discussion
Renal medullary carcinoma (RMC) is a very aggressive (mean survival of less than a year) form of non-clear cell renal carcinoma that is typically seen in young black males with a median age of 19-22 years. Nearly all patients with RMC are symptomatic at presentation with flank pain, abdominal pain, and/or gross hematuria. This tumor is associated with sickle cell trait and is also known as the seventh sickle cell nephropathy. Most patients have metastatic disease at presentation and commonly involved sites include regional lymph nodes, liver, adrenal glands, peritoneum and lungs.
RMC is an epithelial malignant tumor arising in the renal medulla from the collecting ducts which makes collecting duct carcinoma one of the top histologic differential diagnoses. Though RMC and collecting duct carcinoma share similar characteristics, they also have several distinguishing clinicopathologic features. Microscopically, both of these neoplasms may have either a reticular, cribriform, solid, tubular, or adenoid cystic-like morphology with an admixed desmoplastic stroma and neutrophilic infiltration. Tumor cells in RMC occasionally have rhabdoid or sarcomatoid features. The presence of sickled red blood cells is pathognomonic for RMC. Immunohistochemical studies show positive staining for p53, vascular endothelial growth factor (VEGF), PAX8, and hypoxia inducible factor alpha (HIF1α) in RMC. Furthermore, there is loss of INI1 (SMARCB1) expression which is a diagnostically important finding in RMC.
In summary, RMC is an aggressive malignant epithelial neoplasm that is centered in the renal medulla. These tumors typically occur in relatively young patients with sickle cell trait. Almost all patients exhibit symptoms at presentation and the prognosis is poor. Morphologically, these tumors have considerable overlap with collecting duct carcinoma and loss of INI1 (SMARCB1) in RMC is diagnostically useful to separate these two entities.
References
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Holger Moch, Peter A. Humphrey, Thomas M. Ulbright, Victor E. Reuter (Eds): WHO Classification of Tumours of the Urinary System and Male Genital Organs (4th edition).
Patel K, Livni N, Macdonald D. Renal medullary carcinoma, a rare cause of haematuria in sickle cell trait. Br J Haematol. 2006 Jan;132:1.
Srigley JR, Delahunt B. Uncommon and recently described renal carcinomas. Mod Pathol. 2009 Jun;22 Suppl 2:S2-S2
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