Renal collecting duct carcinoma. Report of a case with cytologic findings on fine needle aspiration.

Background: Collecting duct carcinoma (CDC) of the kidney is a rare type of renal cell carcinoma (RCC) of collecting duct origin. Cytologic differentiation of CDC from conventional RCC is important because CDC has a poorer prognosis than the latter.
Case: A 60-year-old male incidentally demonstrated a left renal mass that was hypovascular by angiography. Fine needle aspiration (FNA) revealed numerous clusters of cells arranged in a tubular structure. The cells consisted of highly atypical cells having large nuclei with coarse or vesicular chromatin, prominent nucleoli and lacy or granular cytoplasm. Based on these findings, which were indicative of high grade RCC, he underwent left radical nephrectomy and lymphadenectomy. Histologic and immunohistochemical findings, including anti-high-molecular-weight cytokeratin (HMCK) antibody, confirmed the diagnosis of CDC.
Conclusion: CDC should be added to the differential diagnosis when the result of cytologic examination of a renal mass is suggestive of high grade RCC. These features of FNA smears, together with HMCK immunohistochemistry, can be useful for the cytologic differential diagnosis of renal tumors.