Primitive Neuroectodermal Tumor (PNET) of the kidney: a case report

The surgical specimens were formalin-fixed and paraffin embedded. The sections were stained with routinary H&E. Immunohistochemistry was performed.The immunohistochemical evaluation revealed a diffuse CD99 positivity in the cytoplasm of the neoplastic cells. Pankeratin, cytokeratin AE1/AE3, vimentin, desmin, S100, cromogranin were negative. The clinical presentation and the macroscopic aspect, together with the histological pattern, the cytological characteristic and the cellular immunophenotype addressed the diagnosis towards primary PNET of kidney.Since sometimes it is difficult to discriminate between PNET and Ewing's tumour, we reviewed the difficulties in differential diagnosis. These tumors have a common precursor but the stage of differentiation in which it is blocked is probably different. This could also explain their different biological behaviour and prognosis.The peripheral Primitive Neuroectodermal Tumor (PNET), firstly recognized by Arthur Purdy Stout in 1918, is a member of the family of "small round-cell tumors". Primitive renal localization is very rare. There are almost 50 cases reported in the literature, although it is difficult to estimate the exact number since often it has not been differentiated from Ewing's Sarcoma [1-13]. Renal PNET is more aggressive than in the other sites. It frequently arises during childhood or adolescence, having an aggressive clinical course towards metastatic disease and death. It often recurs locally and metastasises early to regional lymph nodes, lungs, liver, bone and bone marrow, resulting in a poor prognosis. The 5-year disease-free survival rate, for patients presenting well confined extra-skeletal PNET, is around 45–55% and cases with advanced disease at presentation have a median relapse-free survival of only 2 years [1].A 27-year-old woman was referred because of a mild left flank pain and haematuria. Ultrasonography identified a left renal mass homogeneously hyperechogenic in comparison with renal parenchy