Renal neuroendocrine tumour and synchronous pancreas metastasis: histopathological diagnosis using prostatic acid phosphatase.

A woman aged 56 years developed 2 synchronous tumours: one, 1.2 cm in diameter at the head of the pancreas; and the other, 4.0 cm in diameter, at the left side of her horseshoe kidney. Preoperative differential diagnosis of these hypovascular lesions included pancreatic ductal carcinoma (PDC) with renal metastasis, PDC with renal angiomyolipoma, renal cell carcinoma with pancreatic metastasis or PDC and renal cell carcinoma. Following pancreaticoduodenectomy and left nephrectomy, both specimens were diagnosed as grade 2 neuroendocrine tumours (NETs). Immunohistochemistry revealed that both were positive for prostatic acid phosphatase (PAP), which is specific to hindgut-derived NET, including renal NET. Accordingly, the renal tumour was diagnosed as the primary lesion, and the pancreatic tumour as a metastasis. To the best of our knowledge, this is the first report of a renal NET with a synchronous pancreas metastasis. Immunohistochemical staining for PAP was a useful diagnostic marker for synchronous NETs in the kidney and pancreas.