# Primary Renal Small Cell Neuroendocrine Carcinoma With Inferior Vena Cava Tumor Thrombus: A Report of a Rare Case

## TL;DR

A rare case of aggressive kidney cancer in a young man highlights the fast progression and poor outcomes of primary renal small cell neuroendocrine carcinoma.

## Contribution

This paper reports a rare case of primary renal small cell neuroendocrine carcinoma with IVC tumor thrombus and rapid progression in a young patient.

## Key findings

- The patient had a high-grade small cell neuroendocrine carcinoma with IVC tumor thrombus and extensive necrosis.
- Despite surgery and chemotherapy, the patient developed liver metastases and died nine months postoperatively.
- The case emphasizes the aggressive nature and poor prognosis of primary renal SCNC, even in young individuals.

## 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.