DISCUSSION
LMS is a malignant tumor originating from smooth muscle cells and ranks among the most prevalent subtypes of soft tissue sarcomas. It typically occurs in older individuals, particularly those in their 60s and 70s. The tumor primarily develops in the extremities, abdomen, retroperitoneum, and uterus. Primary LMS of the kidney is a rare tumor5.
Previous studies have shown that primary renal LMS is more common in older individuals, typically in their 60s. However, our patient was relatively younger, presenting in her 40s6. The clinical presentation of renal LMS is variable and mostly overlapped with that of other renal neoplasms like RCC. Symptoms typically manifest with the expansion of the tumor, leading to the compression of surrounding structure. These symptoms include the presence of abdominal mass, lumbar pain, and hematuria, as well as systemic symptoms like nausea, vomiting, and abdominal pain1. A prior case series of 10 patients with renal LMS reported lumbar pain as the most common symptom (60%)1.
Radiologically, renal leiomyosarcomas appear as well-circumscribed, expansile, and heterogeneously-enhancing solid masses on CT scans. These tumors usually project from the kidney in an exophytic fashion. However, these findings are not specific, and a definitive histopathological diagnosis is essential to rule out renal cell carcinoma and other tumors7.
Grossly, LMS resembles leiomyoma presenting as a well-defined tumor with a whorled appearance on the cut surface. However, LMS is fleshier and typically shows areas of necrosis, hemorrhage, and cystic changes. At a microscopic level, frequent mitoses, necrosis, and increased nuclear pleomorphism are more indicative of LMS8.
Histologically, renal LMS must be distinguished from sarcomatoid RCC, leiomyoma, and angiomyolipoma. Sarcomatoid differentiation in RCC lacks the typical alternating fascicles seen in LMS and predominantly comprises pleomorphic cells, while LMS exhibits a cellular resemblance to smooth muscle cells8. Immunohistochemistry plays a crucial role in distinguishing between sarcomatoid RCC and LMS. LMS exhibit myoid marker expression and lack cytokeratin positivity. Previous studies have reported immunohistochemical positivity rates of 100% for vimentin, 90% for desmin, and 80% for SMA1. However, sarcomatoid renal cell carcinomas may not consistently exhibit cytokeratin positivity and could express SMA. Similarly, some leiomyosarcomas may display cytokeratin and epithelial muscle antigen (EMA) expression9,10. In the latter situation, the presence of desmin aids diagnosis as it is positive in leiomyosarcoma but not in sarcomatoid carcinoma11. In our case, a typical spindle cell tumor arranged in interlacing fascicles in conjunction with immunohistochemistry made diagnosis possible. Renal angiomyolipoma should also be included in the assessment of smooth muscle tumors of the kidney. In renal angiomyolipoma, fascicles of smooth muscle cells are interspersed with mature adipose tissue and thick-walled blood vessels. Furthermore, angiomyolipoma shows positivity for melanocytic markers, including HMB-45, which can aid in diagnosis of challenging cases12,13 .
Renal LMS is an aggressive tumor with the most common site for distant metastasis being liver, lung, and bone14. The prognosis of renal LMS is generally poor as compared to other renal neoplasms with a median overall survival of 25 months and a 5-year overall survival rate of 25%1. The tumor grade and the effectiveness of the operative treatment are the independent prognostic factors for long-term survival1. Radical nephrectomy is the preferred treatment for renal LMS and offers better overall prognostic value. The use of adjuvant/neo-adjuvant chemotherapy/radiotherapy remains controversial, although sporadic reports suggest potential benefits in reducing tumor recurrence and achieving long-term survival15 .