The patient is an 64 year old white male who presented with left sided back pain. Imaging showed a left perinephric retroperitoneal hematoma and a left renal lower pole cystic lesion with hemorrhage. Additional imaging showed numerous pulmonary lesions. A An endobronchial ultrasound guided fine needle aspiration was scheduled.

The concern is a primary renal malignancy with metastatic disease to lungs. An endobronchial ultrasound guided FNA is scheduled. An onsite rapid diagnosis by cytology was scheduled.

CytologicallyYoursCoW20131209Cytology2.jpg|20x magnification of a 4R lymph node. This is a cellular specimen with groups of cells along what appear to be a papillary or papillary-like structure. Single cells are also dispersed in the background. The cells are haphazardly arranged.CytologicallyYoursCoW20131209Cytology3.jpg|40x magnification of a 4R lymph node. On higher power, the nuclei appear mildly atypical and the cytoplasm is delicate and finely vacuolated. The nuclear contours are somewhat irregular.CytologicallyYoursCoW20131209Cytology4.jpg|Cell block of 4R lymph node. The cytoplasm does not appear as vacuolated on alcohol fixed cell block material, but the nuclei are relatively uniform and monotonous, but somewhat atypical.  </gallery> ===Immunohistochemistry===<gallery heights="250px" widths="250px">

* <spoiler text="What is your differential diagnosis?">These groups of cells demonstrate malignant appearing cells in a background of an otherwise benign appearing lymphoid background. The atypical cells are scattered, with large nucleoli and several binucleate forms. In addition, there seem to other immunohistochemical stains that would be an increased number of eosinophils applicable in the background. The differential diagnosis includes Hodgkin lymphoma; however, the possibility of the large atypical cells being melanoma cannot be ruled out. </spoilerthis case?">* <spoiler text="What ancillary tests would you recommend?">For this patient, we recommended that the radiologist perform a biopsy of the lesion so that it could be sent for immunohistochemical workup. Since the overall percentage of the atypical cells were low, we were worried that a cell block would not contain enough of the malignant cells for additional stains. We also sent the lymph node for flow since a hematologic malignancy was suspected; however, with Hodgkin lymphoma, we don't expect any diagnostic findings from flow cytometry.</spoiler>RCC*CD10*PAX2* <spoiler text="What immunohistochemical stains would you do?">CD15, CD30, and PAX5 would stain tumor cells in Hodkin lymphoma. Mart1, HMB45, and S100 could be used to rule out melanoma. Other additional stain in a lymphoma versus melanoma workup might include CD3, CD20, and keratin.Kidney specific antigen</spoiler>

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* '''Positive for malignancy, the differential Rapid diagnosis includes melanoma and Hodgkin lymphoma''': Non-small cell carcinoma.* Final diagnosis: Renal cell carcinoma.