Spindle Cell Renal Neoplasms: A Pathological Case Report on Primary Renal Leiomyosarcoma and Sarcomatoid Renal Cell Carcinoma.

Renal oncopathology in adults, as a field of pathology, is dominated by a single entity - clear cell renal cell carcinoma (RCC) with other entries, such as urothelial carcinoma of the renal pelvis, angiosarcoma, and others being extremely rare. Herein, we report two histopathological cases with differential diagnoses of spindle cell renal neoplasms. The first patient, a 42-year-old male, presented with new-onset right-sided abdominal flank pain, and imaging showed a 12 cm renal tumor. Histopathology showed a spindle cell neoplasm, with significant mitotic activity and giant cell, with immunohistochemistry being positive for caldesmon and vimentin, focally for smooth muscle actin (SMA). No reaction was noted for pan-cytokeratin (CK AE1/AE3), epithelial membrane antigen (EMA), cytokeratin (CK) 7, cluster of differentiation (CD) 117, soluble 100 protein (S100), human melanoma black (HMB) 45, Melan A, CD10, and desmin. Due to peculiar histomorphology and the immunophenotype, the tumor was interpreted as primary renal leiomyosarcoma. Due to continuous outpatient consultations, treatment initiation was delayed, and three months later, the patient had already developed an 87 mm local recurrence and liver metastasis. The second patient, a 53-year-old male, presented to our institution for consultation of an already excised renal tumor, diagnosed as an incidental finding on a prophylactic abdominal ultrasound. The tumor presented for consultation histologically grew as intertwining bundles of spindle cells with polymorphic hyperchromic nuclei with prominent nucleoli and had extensive areas with necrosis. Immunohistochemically, the tumor diffusely expressed CK AE1/AE3 and caldesmon and had a patchy reaction for EMA and CD10. The SMA, desmin, CD117, and CK7 reactions were negative; hence, the tumor was interpreted as a spindle cell variety (sub-type) of clear RCC.