The clinical symptoms are diverse, non-specific, dependent on the location of the tumor, the growth rate, and the development of collateral blood flow
[6]. When leiomyosarcomas develop in the superior vena cava segment, symptoms manifest as Budd–Chiari syndrome with hepatomegaly, jaundice, ascites, and nausea. In the middle segment, the symptoms are associated with abdominal discomfort and sometimes related to vascular compromise (e.g., edema of the lower limbs)
[14]. In the inferior segment, the symptoms appear relatively late (e.g., edema, nausea, and back pain)
[15][16]. Rarer presenting symptoms are recurrent pulmonary embolisms and metastases. LMSs may remain asymptomatic and are often incidentally diagnosed
[11].
Leiomyosarcomas have a complex karyotype with complex numeric and structural anomalies, and multiple genes have been implicated in its pathogenesis
[17], with significant mutational heterogeneity and frequent copy number variations with no characteristic chromosomal rearrangements
[18]. In a study by Chudasama et al., chromothripsis was reported in 35% of LMSs. Losses of chromosome regions encoding for tumor suppressor genes such as
TP53,
PTEN,
CDH1, and
MYOCD have been reported
[18][19], as well as genes involved in DNA homologous recombination repair (
BRCA2 and
ATM are a frequent target of deletions). Other recurrently mutated genes are chromatin modifiers (
RBL2,
DNMT3A, and
KAT6B), cytokine receptors (
ALK,
FGFR2,
FLT3, and
LIFR), and transcriptional regulators (
PAX3,
FOXO1,
CDX2, and
SUFU)
[18].
Radiology is essential for the diagnosis, and since the symptoms are rather unspecific, the clinical differential diagnosis is broad, encompassing entities such as liposarcomas and lymphomas
[20]. Invariably, the clinician will order an imaging exam such as ultrasonography (US), computerized tomography (CT), magnetic resonance imaging (MRI), or positron emission tomography (PET). US is rather unspecific
[21], so CT is usually the method of choice for the first approach, enabling imaging-guided biopsy
[22][23].
6. Gross and Histologic Features
On gross examination, the majority are extraluminal (76%), with minimal or even absent luminal growth. Tumor size can range from 2 to 30 cm
[8][9].
Histologically, the cells are elongated in shape, with abundant and eosinophilic cytoplasm, centrally placed nuclei, and blunt-ended edges, sometimes called “cigar-shaped”. Architecturally, the cells are arranged in fascicles
[1]. Cytoplasmatic and perinuclear haloes are frequently observed
[29]. An example can be seen in
Figure 1.
Figure 1. Leiomyosarcoma composed of cells with a fascicular architecture. The tumor cells are elongated with an eosinophilic cytoplasm. The cells, although atypical, resemble normal smooth cells, indicating mild atypia.
At higher magnification, longitudinally oriented myofibrils are a common characteristic. They can clump, giving a clotted appearance of the cytoplasm
[7].
As leiomyosarcomas become less differentiated, they lose the resemblance to the normal counterpart. In well-differentiated tumors, the cells are arranged in fascicles, there is mild nuclear polymorphism, and nuclei are centrally located and have a low mitotic rate. In moderately differentiated tumors, the mitotic rate, nuclear polymorphism, and nuclear hyperchromasia are increased. In higher grade tumors, the nuclei often lose the central location, and a fascicular architecture and multinucleated cells are common
[8].
This kind of cellular changes can be seen in Figure 2 and Figure 3.
Figure 2. In this leiomyosarcoma, there is a pronounced atypia with pseudoinclusions and pleomorphic, hyperchromatic, and bizarre nuclei. The preserved vascular lumen can be recognized in the central region of the photo (arrow).
Figure 3. In this tumor, the cells are markedly pleomorphic with multinucleation.
Morphologically, there seems to be no histologic difference between vascular LMS and other types of soft tissue LMS
[29]. The intimal layer is usually intact, but protrusions into the lumen can also be seen
[29].
Immunohistochemistry is helpful in diagnosing leiomyosarcoma and is based on demonstrating myoid differentiation with muscle markers. α-smooth muscle actin (α-SMA), desmin, heavy chain muscle actin, and h-caldesmon, which are myoid markers, are expressed in leiomyosarcomas
[30]. α-SMA and muscle-specific actin are considered the most sensitive markers
[31]. Desmin is expressed in around 70% of leiomyosarcomas
[32][33][34]. It is important to take into consideration not only the expression but also the type of expression of these antibodies: diffuse expression of desmin is indicative of myoid differentiation, but the focal expression of actin or desmin can also be found in myofibroblasts
[35][36]. An example of the immunostaining is represented in
Figure 4.
Figure 4. Diffuse staining for α-SMA (left side) and desmin (right side). Abbreviations: α-SMA—α-smooth muscle actin.
There are interesting differences in the immunostaining characteristics of leiomyosarcomas arising from vascular smooth muscle compared to leiomyosarcomas from different locations. Vascular leiomyosarcomas are more often desmin negative and h-caldesmon positive than leiomyosarcomas arising from soft tissue
[36][37].
The expression of keratins, which is usually regarded as evidence of epithelial differentiation, can be detected in leiomyosarcomas
[37]. A cross-reaction with the antibodies used to detect cytokeratins was first suspected to be the cause of immunoreactivity, but it has been demonstrated that cytokeratins are present both in non-neoplastic smooth muscle and in smooth muscle tumors
[38][39]. The expression of cytokeratins is limited to low molecular weight keratins
[40]. Epithelial membrane antigen (EMA) immunoreactivity can occur in up to 45–60% of cases. When present, staining for cytokeratins is usually focal, but diffuse expression was seen in 11% of cytokeratins and 6% with EMA
[37][40]. A dot-like pattern of cytokeratin expression has been described, and it is associated, at least focally, with a diffuse or a fibrillary pattern
[37]. There is no correlation between the expression of cytokeratins and the location, sex, age, histological grade, and histological features of LMS, but EMA expression is more common in vascular LMS when compared to LMS of the soft tissue, skin, and uterus
[37].
CD34
[41], S100
[42], and HMB45
[43] can also be expressed. Estrogen and progesterone receptors were previously suggested as adjunct (and helpful) markers to distinguish between retroperitoneal leiomyosarcomas and leiomiomas
[44], but it was found that they can be expressed in both uterine and extrauterine LMS
[45][46], therefore not being useful in this distinction.
Histologically, the differential diagnosis for leiomyosarcoma can be extensive, including other spindle cell lesions such as malignant peripheral nerve sheath tumors, synovial sarcomas, leiomyomas, schwannomas, benign cellular myofibroblastic tumors, gastrointestinal stromal tumor, synovial sarcoma, and inflammatory myofibroblastic tumors, as well as other high-grade malignancies, in poorly differentiated cases.