The specimen consists of large groups of malignant cells in sheets and in papillary formations with fibrovascular cores. The cytoplasm is fairly abundant and well defined with clearing. The nuclei are finely granular with inconspicuous nucleoli. IHC stains (not shown) are positive for AE1-3, CK7, AMA-racemase, CD10 and vimentin. Immunostains for RCC, p63, CK 903, TTF-1, thyroglobulin, CD20, ER and PAX2 are negative. Mucin stain is negative.
The patient had a renal cell carcinoma (RCC) in 1998, a transitional cell carcinoma (TCC) of the ureter in 2002 and she is a heavy smoker. The differential diagnosis includes a metastatic papillary RCC, a metastatic TCC and a metastatic papillary adenocarcinoma of the lung. TCCs usually express high molecular weight cytokeratins and p63-protein, and are negative for vimentin and Racemase; papillary lung adenocarcinomas usually express TTF-1 and show mucin production, and are negative for vimentin and Racemase. Although, there is no expression of RCC, the rest of the immunophenotype could be consistent with a papillary RCC (positivity for CK 7, Racemase, vimentin and CD10). Therefore, the histological features are in favour of a metastatic papillary renal cell carcinoma.