Primary ewing sarcoma/primitive neuroectodermal tumor of the kidney

Background: Primary renal Ewing/PNET (primitive neuroectodermal tumor) is a rare yet highly aggressive tumor affecting mainly the young population. The first case described of primary renal Ewing/PNET was in 1975 by Seemayer et al. Ever since then, this entity has been a dilemma for pathologists to diagnose. Both clinical presentation and radiological imaging are nonspecific; patients are generally presenting with nonspecific symptoms such as abdominal mass/pain or hematuria and with radiology that shows a heterogeneous renal mass. Also, under the microscope, the pathologist is faced with a sea of tumor cells having small round blue cell morphology. Case presentation: A 16 years old male, presented to the emergency department of King Fahd University Hospital with gross painless hematuria and right flank pain for the last two months. Contrast-enhanced computerized tomography scan (CT-scan) showed a large heterogeneous right kidney mass with a large central cystic component. Also, a left subpleural lung nodule and para-aortic lymphadenopathy were identified. The patient underwent radical nephrectomy. Under the microscopic, a hypercellular lesion consisting of solid sheets of small blue round cells was identified. The immunohistochemical profile of the neoplastic cells showed positive reactivity for CD99 (diffuse membranous staining), S100, and Vimentin. Fluorescent in situ hybridization (FISH) analysis of EWSR1 break-apart showed evidence of a 22q12 rearrangement. So, the final diagnosis of primary kidney Ewing sarcoma was established based on clinical, pathological, and molecular results. He received five cycles of adjuvant chemotherapy. The patient has been in regular follow-up CT scans, which has been showing no new lesions, the last of which was done January 2020. Conclusion: We report this case of renal Ewing/PNET to enrich the pool of reported cases in the literature of this rare entity. These tumors, in general, have unfavorable prognosis. Early accurate diagnosis and appropriate management, can have a significant impact on the patient prognosis. Fortunately, like in the presented case, the patient had complete remission, which is rare for this tumor. Thus, we emphasize that pathologists and clinicians should have a low threshold of suspicion for diagnosing this entity, especially in this age group.