Answer: Renal medullary carcinoma

Histology: This is a highly aggressive tumor associated with extensive necrosis. The tumor features high grade nuclei which are generally vesicular with prominent nucleoli. In some areas there is a suggestion of hyaline intracytoplasmic inclusions, yielding a “rhabdoid” cytology. The tumor has a cribriform and gland-forming architecture, and is associated with a desmoplastic reaction.
Extravasated amongst the tumor cells are red blood cells which are focally sickled. The diagnosis was confirmed by hemoglobin electrophoresis, which revealed that the patient had sickle cell trait.

Discussion: Metastatic carcinoma would be extremely unlikely in a patient at this age, but would be more of a concern in an adult patient. Clear cell sarcoma of the kidney is also an aggressive neoplasm, but would lack the gland formation and prominent nucleoli of this tumor. Papillary renal cell carcinoma has a solid glandular variant, but lacks the high-grade cytology and desmoplastic stroma associated with the current lesion.

Renal medullary carcinoma is a highly lethal cancer that almost exclusively strikes children and young adults with sickle cell trait hemoglobinopathy. Some consider it to be a variant of collecting duct carcinoma. Microscopically, the lesion has an invasive border and its architecture ranges from reticular or yolk sac-like to gland forming. The cells frequently have rhabdoid-type cytology, which raises the differential diagnosis of rhabdoid tumor of the kidney; the latter though is almost exclusively a tumor of infants. Unfortunately, renal medullary carcinoma is a highly lethal tumor with mean survival measured in weeks.

Reference(s):
Am J Surg Path 1995; 19:1-11