Metastatic lung adenocarcinoma to the kidney diagnosed by urine cytology: a case report.

Background: Although lung cancer is the solid tumor which most frequently metastasizes to the kidney, metastatic pulmonary adenocarcinoma detected by urine cytology examination is exceedingly rare.

Case: A 52-year-old woman presented with gross hematuria. Urine cytology revealed numerous crowded, overlapped 3-dimensional clusters with occasional papillary and luminal formations. The tumor nuclei were uniformly enlarged with smooth oval contours, regular nuclear membranes, finely granular chromatin, and prominent nucleoli. Numerous clear, intracytoplasmic vacuoles were noted. Urine fluorescence in situ hybridization (FISH) examination was abnormal. Positive immunohistochemical thyroglobulin transcription factor-1 and Napsin-A staining of a renal calyx biopsy confirmed the diagnosis of metastatic lung cancer.

Conclusion: Although rare, metastatic lung adenocarcinoma in urine has characteristic cytomorphologic findings which appear distinct from the more commonly encountered urothelial carcinoma. Differentiation from other metastatic malignancies may be more problematic and will likely require immunohistochemical confirmation. Metastatic lung cancer may also cause abnormal urine FISH results and thus may be misdiagnosed as urothelial cancer. Therefore, this ancillary testing modality must be employed with caution in the setting of metastatic disease.