In terms of its presenting symptoms, leiomyosarcoma mimics other renal malignancies. There are no specific presenting symptoms that can differentiate renal LMS from other renal malignancies. As with renal cell carcinoma, symptoms occur relatively late in the course of the disease, and patients present with hematuria, abdominal pain, and an abdominal mass.[7] Moazzam et al. reported a case of renal leiomyosarcoma presenting with spontaneous retroperitoneal hemorrhage and hypotension.[11]

Advances in computerized tomography (CT), magnetic resonance imaging (MRI), and other specialized imaging techniques have created great improvements in the diagnosis of renal cell carcinoma (RCC), benign renal neoplasms, and in characterizing the level of aggressiveness of RCC subtypes, which informs management decisions in these tumors. However, renal leiomyosarcoma is rare and does not have known specific imaging characteristics. Unlike other retroperitoneal tumors, CT is limited in the evaluation of renal LMS. The most important differential of renal LMS is renal cell carcinoma, which cannot be reliably differentiated with any radiological technique.[12][13] Due to this limitation, CT-guided core needle biopsy is strongly recommended for histopathological diagnosis of the tumor, which is critical to planning appropriate therapy.[5][12] Image-guided percutaneous renal mass biopsy is a safe procedure with a high degree of diagnostic accuracy.[14]

Leiomyosarcoma is the most common histological subtype and accounts for 50-60% of total renal sarcomas. However, renal leiomyosarcoma is still a remarkably rare tumor.[15] As mentioned above, needle core biopsy of the tumor under image guidance is recommended to make a definitive diagnosis and to guide surgical treatment and neoadjuvant therapy. Clinically significant complications for preoperative core biopsy are rare,[14], and concerns regarding the risk of needle-track seeding, micro-metastasis, and/or acute intra-abdominal conditions appear unwarranted based on clinical data.[16] 

There is no consensus on the role of neoadjuvant or adjuvant radio/chemotherapy in the management of renal LMS.[5] Due to the relatively low incidence of renal leiomyosarcoma, there are no randomized controlled trials to dictate treatment and are generally extrapolated from other retroperitoneal/intra-abdominal sarcomas and case reports. Prior to the initiation of therapy, all patients should be evaluated and managed by an interprofessional team with expertise and experience in sarcomas. For all patients, we should suggest participation in ongoing clinical trials, where available. Surgical resection has traditionally been the only potentially curative approach. The currently recommended treatment for resectable tumors is complete surgical excision of the tumor with negative margins. Due to the significant proportion of aggressive leiomyosarcomas that tend to recur locally, radical nephrectomy is a superior management option that provides better oncologic control.[17] Demir et al. described nephron-sparing surgery with no sign of recurrence, but the tumor was low grade with no change in size for 3 years.[17] If the surgeon anticipates a grossly incomplete resection, intraoperative radiation therapy (IORT) results in excellent local control and survival, with acceptable morbidity.[18]

If protocol therapy is not available or the patient is not eligible, the treatment approach differs based upon grade and histology. For patients with intermediate and high-grade tumors, large tumors, and the risk of distant metastatic disease is high, then preoperative RT alone, preoperative chemotherapy (with postoperative RT), or preoperative chemoradiotherapy are all acceptable options. Responders to neoadjuvant treatments tend to do better than nonresponders, whether this reflects the impact of chemotherapy/RT or disease biology. In patients with large, high-grade leiomyosarcomas and dedifferentiated liposarcomas, the addition of neoadjuvant chemotherapy to surgery is being investigated in a randomized trial (STRASS-2) conducted by the European Organization for Research and Treatment of Cancer (EORTC).[19]

Neoadjuvant radiotherapy is generally administered while it is not indicated postoperatively in R0 (tumor resection with negative macro and microscopic margins). Adjuvant chemotherapy is recommended in cases of R2 resections (tumors with positive macro and microscopic resection margins) as well as in unresectable and metastatic disease.[5] Anthracycline/ifosfamide-containing chemotherapy is usually the preferred regimen. Single-institution phase II study by Mahmood et al. investigated the safety and efficacy of sunitinib malate in three common soft tissue sarcomas (STS) subtypes among patients with documented unresectable or metastatic disease. The median progression-free survival was 4.2 months, and the median overall survival was 10.1 months among patients with LMS. Further investigation with multicentric, phase 3 studies is warranted.[20]

Although renal LMS is the most common primary renal sarcoma (50 to 60%),[5] it is still a very rare entity, and other neoplasms must be ruled out before making the diagnosis of primary renal LMS. 

Retroperitoneal leiomyosarcoma, involving the kidney should be ruled out before making the diagnosis of primary renal LMS for which radiological techniques can play an important role in defining the boundaries of the lesion.

Sarcomatoid carcinoma of the kidney, arising from renal cell carcinoma or less commonly from urothelial carcinoma, is perhaps the most important histopathologic differential diagnosis when dealing with a spindle cell renal tumor. Histological evaluation of sarcomatoid carcinoma often shows a malignant epithelial component, in contrast to the uniform fascicular architecture of leiomyosarcoma. In limited samples, where only spindle cell component is encountered, immunohistochemistry can help as the spindle cell component of sarcomatoid carcinoma is typically positive for keratin and negative for actin, while the reverse is true for leiomyosarcoma.[1]

Angiomyolipoma, a tumor of perivascular epithelioid cells, can mimic renal LMS histologically. The histological finding of mature adipose tissue with thick hyalinized blood vessels favors angiomyolipoma. But, if only spindle cell component predominates with significant atypia, immunohistochemical reactivity for HMB-45 (a melanocytic marker) is seen in angiomyolipoma but is negative in LMS, which is helpful in this differential.[1]

Renal leiomyomas are the benign counterparts of leiomyosarcoma, and they are exceedingly rare neoplasms. Radiological techniques are not sufficient to distinguish them from leiomyosarcoma, and histological evaluation of the tumor is necessary to make the definitive diagnosis, which shows the fascicular arrangement of benign smooth muscles with no atypia, or necrosis and very rare or absent mitosis.[21] It is important to note that many leiomyosarcomas have focal areas that resemble leiomyoma, and adequate sampling of the tumor is crucial for an accurate diagnosis.

Staging is done based on the American joint committee on Cancer (AJCC) staging system for soft tissue sarcoma of the abdomen and thoracic visceral organs (8th edition).

Renal LMS carries a poor prognosis with a median overall survival of 25 months. Among soft-tissue sarcomas, the stage is the most important prognostic factor. Other factors include histological subtype, grade, age of the patient, and gender.[22] The rate of local recurrence and the risk of metastasis is determined by the grade of tumor and inferior vena cava extension.[5]

Rare cases presenting with spontaneous retroperitoneal hemorrhage and hypotension have been reported in the literature. In a case series of 67 patients with renal vein LMS, 50% of the patients experienced disease progression despite treatment. Metastasis to distant body sites (liver>lungs>bones>soft tissue) occurred in 30% of patients. The rate of local recurrence was 4.5%, while 15% of the patients experienced combined local recurrence and distant metastasis.[5] Intra-renal LMS appears to behave in the same manner.[1]

Renal LMS is a rare, but aggressive malignancy which carries an overall poor prognosis. There are no established risk factors, so prevention is not an option. Many studies suggest patients succumb to the disease, this observation was common in the patients with intermediate to high-grade tumors. Patient education is important as the rate of local recurrence of this tumor in the first 2 years is high, good compliance with regular follow-up can help to identify the recurrence at an early stage and improves the outcome.

Renal leiomyosarcoma is a rare, aggressive malignancy that carries an overall poor prognosis. Its clinical presentation is not different from that of the far more common renal cell carcinoma with hematuria, flank pain, and an abdominal mass. Radiologists play a crucial role in the diagnosis, not simply by identifying the renal mass, but by performing an image-guided percutaneous biopsy to obtain adequate and representative tissue for biopsy. Radiologists also select the imaging modalities appropriate for staging the disease. Histopathologists examine the biopsy tissue using routine microscopic and immunohistochemical techniques to make a specific diagnosis and assign a grade to the tumor. The grade is another important prognostic indicator. Surgeons perform radical nephrectomy, which is the recommended definitive treatment. Medical oncologists and radiation oncologists may offer additional therapy depending on the margin status as confirmed by the pathologist postoperatively and taking into account the clinical staging. [Level 5]