Answer: Renal medullary carcinoma

Histology: This is an epithelial neoplasm featuring both solid and cribiform growth patterns. Neoplastic cells have vesicular chromatin and prominent nucleoli, and there is a marked neutrophilic infiltrate associated with the neoplasm. The stroma between the nests of tumor cells is desmoplastic. One can appreciate areas of sinus lymphatic invasion beneath the renal pelvic urothelium. This lesion presented with metastatic disease to the supraclavicular lymph nodes. The patient was subsequently found to have sickle cell trait, which is tightly linked to renal medullary carcinoma.

Discussion: Wilms tumor would demonstrate more primitive epithelial cells and frequently contain blastemal and spindle cell areas. Clear cell sarcoma of the kidney would feature cells with fine nuclear chromatin without prominent nucleoli, and would not show the cribiform pattern seen in the current case. Congenital mesoblastic neophroma is a spindle cell neoplasm which morphologically overlaps with either infantile fibromatosis (classic type of CMN) or infantile fibrosarcoma (cellular type of CMN).