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 .