A 84-year-old woman with a history of endometrial cancer and multiple comorbidities was admitted to the hospital due to abdominal pain. Contrast-enhanced abdominal computed tomography (CT) showed a heterogeneous mass sized 50 mm × 37 mm × 30 mm emerging from the right kidney (Figure 1A). The preoperative suspicion was metastasis of endometrioid cancer, lymphoma infiltration, or even inflammatory lesions. The patient underwent right radical nephroureterectomy. Macroscopically, a multilobulated mass measuring 76 mm × 45 mm × 35 mm was identified. Cross-sections were gray-white in color and contained areas of necrosis. The tumor extended into the renal parenchyma, infiltrating the renal pelvis and renal sinus fat. Histopathologic examination demonstrated the presence of 2 distinct neoplastic components (Figure 1B)—small cell carcinoma (SCC), which accounted for approximately 85% of the tumor (Figure 1C), and invasive high-grade urothelial carcinoma, which constituted approximately 15% of the tumor (Figure 1D). Neoplastic neuroendocrine cells were positive for synaptophysin (Figure 1E), chromogranin A, and CD56, while the urothelial carcinoma component showed positivity for cytokeratin (CK) AE1/AE3, CK7, CK20, p63 (Figure 1F), and GATA3. Endometrioid cancer metastasis was excluded by immunohistochemistry (Figure 1G). These results supported the diagnosis of combined SCC with an additional component of high-grade urothelial carcinoma. Postoperative CT scan excluded primary lung lesion and revealed pathologic soft-tissue masses in the kidney tumor bed (Figure 1H) and numerous pathologic lymph nodes in the lower part of the neck, upper mediastinum, and retroperitoneal space, which corresponded to dissemination of the neoplastic process. The patient received 6 cycles of chemotherapy with carboplatin and etoposide at 3- to 4-week intervals. On the follow-up CT scan, partial remission of the nodal and infiltrative lesions was observed. Currently, 7 months after the diagnosis, the patient is alive with the disease and in satisfactory general condition.

Figure 1. Combined renal small cell carcinoma (SCC); A – abdominal computed tomography scan, transverse view, showing a pathologic mass emerging from the upper pole of the right kidney (arrow); B – combined renal SCC: SCC (left side) coexisting with high-grade urothelial carcinoma (right side) (hematoxylin and eosin staining, magnification × 100); C – sheet-like growth pattern of SCC with extensive necrosis. The neoplastic cells are round or oval, with scant cytoplasm and indistinct cell borders. The nuclei are hyperchromatic, with dispersed granular chromatin and inconspicuous nucleoli. Mitotic figures and apoptotic bodies are easily observed (hematoxylin and eosin staining [HE], magnification × 100). D – neoplastic cells of urothelial carcinoma are arranged in irregular nests and show high-grade nuclear features, such as nuclear pleomorphism, hyperchromasia, high nuclear to cytoplasmic ratio, and frequent mitotic figures, including abnormal forms (HE, magnification × 100). E – immunohistochemical examination with synaptophysin showing strong and diffuse cytoplasmatic positivity in neuroendocrine component (magnification × 100); F – immunohistochemical examination with p63 antibody showing nuclear diffuse positivity in the urothelial carcinoma neoplastic cells (magnification × 100); G – immunohistochemical examination showing negative immunostaining for anti–estrogen receptor (ER) antibody in both neoplastic components (ER, magnification × 100); H – abdominal computed tomography scan, transverse view, showing pathologic masses in the postoperative area (arrow)

More than 90% of SCCs occur in the lungs; however, the disease is also found in various extrapulmonary sites, including the genitourinary tract. Most SCCs in the genitourinary tract develop in the prostate and urinary bladder. SCC of the kidney is extremely rare, with only a few cases reported in the literature.1-4 Because lung SCC is far more common than renal SCC, metastasis of the primary lung tumor or tumor-to-tumor metastasis of lung cancer should always be excluded during evaluation of SCC in the kidney.1,5 Renal SCC can occur in its pure form or together with high-grade urothelial carcinoma.1,2 There are no pathognomonic clinical symptoms that suggest the presence of SCC. Abdominal pain is the most common finding, affecting nearly 70% of patients.2-4 The diagnosis of SCC is established by light microscopic and immunohistochemical examination of the tumor tissue.2 The clinical behavior of extrapulmonary SCCs is invariably aggressive, with a median survival up to 8 months.2 Patients with renal SCC tend to develop early nodal and disseminated metastatic disease.2 Due to the small number of renal SCC cases, there is no standard treatment protocol available. However, because of unfavorable prognosis, multimodal therapy, including surgery, systemic platinum-based chemotherapy, and radiotherapy has been increasingly used to prolong patient life.2,3 Further investigations on renal SCC may aid in better understanding of this tumor and lead to improved patient survival.