Abstract
Primary renal neuroendocrine tumors (NETs) are exceedingly rare. Among these, small cell neuroendocrine carcinoma (SCNC) represents an aggressive and poorly differentiated subtype, with very few documented cases. We present a case of a 24-year-old male patient who presented with gross hematuria and flank pain. Imaging revealed a large right renal mass with a tumor thrombus extending into the inferior vena cava (IVC). The patient underwent radical nephrectomy, adrenalectomy, and IVC thrombectomy. Histopathological examination confirmed a high-grade small cell neuroendocrine carcinoma with extensive necrosis and vascular invasion. Immunohistochemistry was positive for CD56, synaptophysin, and a high Ki-67 index (~70%). Despite radical surgery and systemic chemotherapy with carboplatin and etoposide, the patient developed liver metastases within three months and succumbed to disease progression nine months postoperatively. This case underscores the rarity and aggressive nature of primary renal SCNC, the clinical significance of IVC tumor thrombus as a poor prognostic factor, and the rapid disease progression that can occur even in young patients. Multimodal therapy remains the mainstay of treatment, but the overall prognosis is poor. Further investigation into molecular characteristics and targeted therapies is urgently needed.